Dear Mark: Is a High Protein Diet Really As Bad for You As Smoking?

It’s about that time, boys and girls. A new “protein kills” study has arrived to throw you into the pit of existential angst and self-doubt you recently managed to crawl out of from the last one. As you may know, I’ve just spent a week in Tulum, Mexico for PrimalCon (which was amazing, by the way, absolutely fantastic) where I managed to avoid most contact with my inbox. Oh, I took a couple glimpses here and there, enough to notice an endless stream of frenzied email subject lines, but I didn’t read the contents until the flight home. I still knew what was coming.

I finally have a little time to dig into this paper (which actually covers two studies) to see if there’s anything we can learn. Let’s jump right in…


A co-worker informed me of a news clip she’d heard regarding an increased cancer risk for those who stick to a high animal protein-based diet. She said that smoking cigarettes is healthier than eating high fat/high protein diet. My first reaction was to chuckle (just another CW media attack against Paleo/Primal) and I did once I read the actual piece in Forbes. I wanted to get your thoughts on it as a lot of the article’s evidence once again seems inconclusive. Seems like there are a lot of caveats.


Right off the bat, we can read the paper and see an important part that the journalists conveniently left out:

Conversely, high protein intake was associated with reduced cancer and overall mortality in respondents over 65, but a 5-fold increase in diabetes mortality across all ages.


Using Cox Proportional Hazard models, we found that high and moderate protein consumption were positively associated with diabetes-related mortality, but not associated with all-cause, CVD, or cancer mortality when subjects at all the ages above 50 were considered.

Huh. From age 50-65, protein modestly increases mortality, especially cancer- and diabetes-related mortality. In ages 50+, though, a high protein intake has no association with all-cause mortality (the most important endpoint), while in ages 65+, high protein is downright protective. The only consistent positive association across all ages is with diabetes mortality. How can this be?

It’s well known that seniors are less efficient at utilizing protein than younger people. Muscle protein synthesis is slightly impaired in the elderly, for example. As such, they need to eat more of it to get the same benefits as the rest of the population. It may be that they also have a higher upper threshold for protein until harm ensues – a higher “protein ceiling.”

Other populations also have higher ceilings. Runners, cyclists, dancers, swimmers, weight lifters (especially weight lifters) all need more protein than the sedentary, just like the seniors. Unfortunately, the authors did not control for exercise. Too bad, because it probably would have modified the relationship between protein intake and mortality in the other age groups.

I think if anything can be taken from this study, it’s that you should only eat as much protein as you require. We likely all have “safe protein ceilings” depending on various factors, like age and activity level. The ceiling is higher the older and more active you are.

Since the connection between diabetes-related mortality and protein persisted even among the older crowd, let’s look at that a little further. Does other research agree that protein is bad for diabetics?

Well, in the most recent meta-analysis dealing with diet and diabetes, researchers concluded that “low-carbohydrate, low-GI, Mediterranean, and high-protein diets are effective in improving various markers of cardiovascular risk in people with diabetes and should be considered in the overall strategy of diabetes management.” They looked at both epidemiology and clinical trials to reach that conclusion, so it’s not clear how protein is increasing diabetes mortality in the current study if the relationship is causal.

I’m not suggesting that you eat all the protein you want as long as you’re exercising or elderly. I’ve even softened my “high-protein” leanings over the years, advocating instead for a more moderate approach. One gram protein per pound of lean tissue is plenty for most active people, and many can get by on half that.

The Mouse Study

Okay, that’s one part of the paper. There was also a study that found both breast cancer and melanoma tumors grew more slowly in mice on a 4-7% protein diet than mice on an 18% protein diet. High protein mice also had higher levels of IGF-1, a growth promoter, and the rate of tumor growth was associated with the amount of IGF-1 secreted. The protein was entirely casein, with a touch of added methionine.

When I saw that they used casein, it reminded me of something from Chris Masterjohn’s analysis of the T. Colin Campbell casein/cancer studies. While high intakes of casein promoted the growth of existing tumors in those rodents, it was also protective against the mutagens that cause the initial appearance of tumors. Protein was protective against cancer until they had it, at which point it accelerated the cancer’s progression. Rodents on the low protein diet were more susceptible to getting cancer after aflatoxin exposure. Once the rodents already had cancer, low protein was protective against further growth.

Does this phenomenon apply to the most recent study? Impossible to tell. The mice were directly injected with melanoma and breast cancer cells, not exposed to a cancer-causing toxin or exposed to high levels of UV radiation. This usually isn’t how cancer develops in the real world, unless we’re talking about mistakenly receiving a cancerous organ transplant. We tend to develop cancer in response to mutagens in the environment.

That said, we can’t discount the results entirely. Getting your protein only from casein is unwise (and unfeasible when eating whole foods). Methionine (an amino acid common in muscle meat which does increase IGF-1) probably should be balanced with glycine (an amino acid common in connective tissue and gelatinous cuts of meat). I think glycine is especially important for a few reasons:

Realize that the Primal eating plan doesn’t prescribe “eating lots of meat.” Instead, we “eat animals,” and animals have bones and gristle and organs and tendons and loins and ribs and shoulders and all kinds of edible bits and pieces with extremely varying amino acid profiles. Over the years, I’ve been emphasizing these “alternative” cuts more and more. The folks profiled in the study’s data sets probably weren’t eating whole animals. The mice definitely weren’t. We largely just eat meat, and I think that should probably change if we want to maintain optimal health and avoid some of the diseases the epidemiology keeps pointing at.

There are also untoward effects of ultra-low protein intakes to consider. While this paper was only concerned with the cancer endpoint, free-living, free-thinking, autonomous humans with hopes, desires, aspirations, and goals aren’t only worried about cancer. We’d certainly prefer not to have cancer, but what if the narrow pursuit of the ultimate anti-carcinogenic diet has unpleasant side effects that affect the enjoyment of our lives?

Consider that low protein diets:

In other words, starving yourself of protein (the mice in the study achieved the protective effects by eating just 4-7% of calories as protein, which qualifies as protein starvation in most books) may reduce tumor growth, but it might make you fatter and weaker, give you brittle bones, prevent you from taking care of yourself in the later years, and make you more susceptible to illness. Oh, and it may even make you more vulnerable to initially getting cancer (if the Campbell casein studies are applicable to people). But that’s all worth it if once you have cancer the tumors grow slightly more slowly, right?

Even IGF-1 isn’t evil. It promotes growth across the board – in muscles and in tumors. Tumors suck, but not everyone has tumors. Everyone does have muscles. IGF-1 secretion also promotes neural growth and resistance to neurological degeneration. In a study mentioned in yesterday’s Weekend Link Love, elderly women improved muscular and cognitive function by eating a diet high in protein derived from red meat and lifting heavy things. Another study found that increased IGF-1 was linked to improved memory and vigor in both middle-aged and elderly subjects. I don’t know about you, but “living long and dropping dead” is all about vigor for me.

Think about it. Vigor. Sure, it’s not exactly a traditional health biomarker, but who’s got it? What kind of older people display vigor?

The sassy centenarian who eats bacon for breakfast every single day.

The old guy with the vise-grip for a handshake.

That old dude surfing with all the guys a third his age.

The 85 year-old great grandmother who shoulders past you at the farmer’s market to get the best leeks.

The old lady who beats you at raquetball.

I will take vigor every single time even if it modestly increases the speed of tumor growth on the off chance I get cancer. That’s just me, though.

Summing Up

As I see it, there are some potential takeaways, keeping in mind that half the paper was based on epidemiology:

Don’t eat more protein than you actually need. Get extra calories from fat and, if activity warrants it, carbs.

Eat the whole animal. Don’t just eat muscle meat, but also bones, ligaments, shanks, cartilage, tails, and organs. Supplementary gelatin is a good idea if you don’t eat the aforementioned foods.

Don’t eat a diet of casein, methionine, soybean oil, corn starch, and sucrose, especially if you have cancer.

And some questions:

High IGF-1 levels are linked to bad things like cancer, but also good things like strong muscles and a sharp mind. How do we balance the two?

Were processed meat and fresh meat lumped together? Is pepperoni pizza “meat”?

What about people younger than 50? They weren’t addressed at all.

How valid is the dietary data? It was gathered by calling people on the phone and asking them what they’d eaten the previous day and whether that was typical of their normal diet. Seems awfully unreliable and prone to human error.

That’s my take. There are many others out there, but this is mine. What do you think?

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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84 thoughts on “Dear Mark: Is a High Protein Diet Really As Bad for You As Smoking?”

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  1. I highly doubt that the damage a high protein diet can do, can compare with the damage from smoking cigarettes. First of all, those two cause very different kinds of damage and can not be compared just like that.
    Any low carb diet can significantly stress and damage the liver regardless of your age, as was proved lots of times with the Atkins diet – and many people fail to take notice that Dr. Atkins, a nutritionist, made up this diet to treat his own weight problems (as far as I remember, he was obese).
    This gave me some food for thought, but cigarettes and meat are just two of the far too many factors that can cause cancer, though I doubt they would cause it directly, so I decide not to put too much emphasis on this and stick to the old one – everything in moderation.
    Thanks for writing!

  2. My take is Toucan Sam followed his nose to the Fruit Loops and the big time pay off from the grain companies again instead of doing a real clinical trial or at least some honest effort at real science. They could probably have monkeys type these things up every few months by now. Atkin’s has some real research I saw posted a while back they have funded with folks under actual medical observation. Maybe someone would like to put their money where their mouth is and go up against that?

  3. “The 85 year old great grandmother who shoulders past you at the farmer’s market to get the best leeks”. Sounds like my farmer’s market.

    1. Hopefully she walks home too. Then I could get back at her by following her home and stealing all the ripe vegetables from her garden while she’s asleep.

  4. Thanks for this Mark. Looking at the the study I found it incredible that scientists can draw conclusions about what caused the death of an entire block of people, after 18 years, by looking at ONE DAY of eating, from memory! What? How the heck could you know if that one day was anything near typical for them, or, what habits may have changed for them the next day, week, month or year? I found this astounding.

  5. In other words unless cancer is a particular concern for you and runs in your family then a diet with modest amount of meat in it is not of great concern? And even if it is a concern for you then considering the otherwise health trade offs that come in a low protein diet then the potential increased cancer risk would probably best be addressed by frequent and regular testing which you ought to be doing anyhow in your circumstances.

  6. Of mice and men: accodring to Denise Minger those mice have been fed with the mouse equivalent of the LFHC SAD, being called ““AIN-93G standard chow.”

    Corn starch (397 g)
    Casein (200 g)
    Maltodextrin (132 g)
    Sucrose (100 g)
    Soybean oil (70 g)
    Cellulose (50 g)

    14% O6-fat, 18% casein, 58% high GI-starch and 10% sugar- does one need to say anything more? I’m wondering what would have happened when they would have given worms, insects herbs, seeds and fruits instead with the same macro proportions?

    1. Then it would be much harder to ensure the ratios are exactly the same for every bite taken by every mouse. This would render the data non-applicacable, because wild mice and normal humans only consume standard chow.

      I suppose it would also be several times as expensive, from 0.003% of study cost to 0.014% (guesstimate).

    2. Lab animal diets should be designed by zoologists (or related field) with extensive field experience.

  7. The carbohydrate content of the diet was I believe 51%. No indication of that being a factor.

    Was the “protein” lean or fatty. Lean animal protein (red meat) is associated with higher blood glucose isn’t it?

    Put these two things and diabetes seems less “surprising.”

    It seems like the added complexity of the study took away from much of whatever value it might purport to allude to.

  8. Well– I have followed a mostly Steffanson diet– I cannnot eat carbs wiithout getting heartburn–unless it’s spinach – salads and the like–so I have Primal Fuel shake for lunch (using no sugar almond milk– and eggs for breakfast with bacon and chicken or steak for dinner with a few veggies.

    I guess (at age 63) feeling 19 and running wind and hill sprints, playing basketball and boxing– and lifiting heavy things occassionally is the benefit of a high protein regimen (at least for me)

    Thanks for breaking down another “study”– we are all individuals and we all respond differently to certain dietary needs– I just need and LOVE high protein.

    PS. Hey Mark, send me a grass fed steak! I’m hungry after reading this!

  9. Am I missing something, or is the entire human portion of this paper based on extrapolating what someone ate on one day into what they ate for the next 18 years? That’s… that’s just crazy. How can that possibly be considered reliable enough data for any kind of serious science? I am baffled.

    1. They’re the same types of folks that try to scare people with the “global warming” hype.
      They’ve got an agenda, and it’s called filling their wallet!

      1. You’re right about folks extrapolating what someone ate on one day into what they ate for the next 18 years. About some folks being falsely scaring people with global warming? Nope, not right at all.Not. At. All.

    2. Well spotted.
      The premise is that what you ate on one day 18 years ago will correlate with the cause of death listed on your death certificate. Science, don’t you know.

      Another glaring flaw – absolute protein consumption is ignored.
      We don’t know anything about HOW MUCH protein anyone ate on that fateful day.
      We only know what % of energy it represented.
      And if alcohol wasn’t measured, and if alcohol replaces starch in the diet of alcoholics, as seems to be the case, then the high protein % may have included alcoholics.
      There is also the possibility that different generations tell different types of lies, or make different kinds of errors, in diet questionnaires. I think there have been studies into honesty of different age-groups that shows this effect.
      If we were to take this study seriously, we would have to consider all this and more.

  10. This is just another of the long line of articles attempting to meat-bash, only they aren’t using the right meat! If only they’d do a study using grass-fed, pastured meat…but no. No Big Food conglomerate would fund it, and neither wouid the politics-ridden NHS.

    It sounds like this study was funded by Big Soy (if there is such a thing).

  11. “Don’t eat more protein than you actually need” seems a bit ambiguous if you don’t know how much you actually need. How does one know how much “lean tissue” one has?

    1. Paraphrasing Justice Potter Stewart:

      I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description [“lean tissue”]; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it…

    2. it is easy. if you crave proteins, eat them. if you don’t then don’t. just don’t force them down for whatever reason. protein intake is pretty tightly regulated by the body. you can’t deliberately under or over eat proteins without having to fight your body. resisting cravings or forcing down stuff against the puke reflex, that is. this of course if you eat real foods. if you drink protein shakes, all bets are off.

  12. “Don’t eat a diet of casein, methionine, soybean oil, corn starch, and sucrose, especially if you have cancer.”

    HA! OMG I’m still laughing at this line!!

  13. Longo apparently has interest in a company which makes soy protein.

  14. Take a look at the articles written by Layne Norton, he has a PhD in Nutritional Sciences with a thesis on muscle protein synthesis.

    He writes with a lot of scientific facts and proofs backing it, he’s really good on the protein subject.

  15. I’m a diabetic. Before finding the low carb/primal way of life, I was over 200 pounds, took two blood pressure meds and three diabetes meds twice a day. 2-1/2 years later, even with a year-long sidetrack dealing with thyroid cancer, I’m 60 pounds less, and I take 1 diabetes med. My A1C is 5.6, which is the same as my tall, skinny, very healthy husband. For me, this way of life has been a life-saver. I’ll be 59 in a few weeks and I want to be that 85 year old great grandmother who shoulders past you at the farmer’s market to get the best leeks, so I’ll just keep doing what I’m doing and the heck with these off-the-wall research studies.

    1. Also another fantastic British review from Zoe Harcomb

      The best part has to be this:

      “The study claims to have adjusted for protein in general vs. animal protein to conclude that animal protein is the harmful factor and not protein per se. Call me suspicious, but I always check for conflicts of interest and the lead researcher, Dr Longo, has declared interests in (actually, he’s the founder of) L-Nutra – a company that makes ProLon™ – an entirely plant based meal replacement product.”


  16. If there is any increased mortality due to eating meat, can it be because of the source of most meat? If the pigs and cows are being fed crap and hormones and drugs then so are we. I am wondering if the study would have the same results if all the animals were pastured in a clean environment w/o drugs and hormones. I cannot believe that an adequate protein diet lessens our life span. That just makes no sense. I DO believe we have to be careful about the source and handling of ALL food we injest, however.

  17. I scrolled right down but I think I can guess how this post will go.. evidence presented against protein, that evidence refuted and evidence given for the benefits of extra protein, and then “no, nothing to worry about”. Well, now time to read and see.

    1. Not exactly that linear. Nicely done post that jumps around a bit compared to my predicted formulaic approach and cohesively produces a valuable lesson (and reminder) about eating animals.
      I’m thinking of getting some supplemental gelatin soon and visiting a butcher shop to see what non-muscle meat is available. I was thinking of making my own primal candies using gelatin, a natural sweetener, and possible other ingredients including coconut oil, cacao, and strong juices like lemon. I also want to try head cheese. I like gristle, marrow, and edible bones, the latter typically from salmon and sardines.
      Recently I read a book about Edgar Cayce (The Sleeping Prophet), a guy who would fall asleep and diagnose diseases and tell people how to cure them and also make predictions and provide information he logically shouldn’t have been able to. Apparently on health “readings” the information he provided was accurate at least 97% of the time.
      His diet recommendations varied for different people and he did recommend grains (advice I’ll largely ignore) but also recommended eating seafood regular, especially shellfish, organ meat including brains and liver, and salads with gelatin because apparently it helps the glands use micro-nutrients.

      1. My thought is that people that think about what they out in their mouths (food!) are generally healthier than people that don’t.

        1. I’m inclined to share that assumption.
          I forgot to mention something about Cayce’s dietary recommendations that led me to write about him here in the first place, that being that he says two to three almonds a day is an effective defense against getting cancer. The book said it might have something to do with the lutein. Cayce says an almond a day is a more accurate line of advice for protecting health than an apple a day. Mark’s Daily Almond.. MDA – still works. Shall I begin a petition? I remember someone else joking it might make more sense replacing apple with macadamia nut, or something else, pastured egg yolk maybe.
          I’m not going to unquestioningly be enslaved to all Cayce’s recommendations but since he was right about so many matters of health I believe his advice is worth reading into. Some of it is primal (or primal compatible) and backed up with science.

  18. I freaked out a little when I first saw the article, too, but–then I realized they were talking about percent of calories in a diet from protein (not grams per day or something like that). I’m new at trying to figure all this out and I might be kinda dumb here, but can’t you reduce the percentage of your calories from protein by simply taking in more fat calories? Wouldn’t the same meal, with some added fat, have a lower percentage of calories from protein, even without actually reducing the protein? And therefore, if people who ate a higher percentage of calories from protein did have an increase in cancer, couldn’t that simply mean they weren’t eating enough fat? So it could just as easily be interpreted as, the low-fat trend caused the cancer? (I’m not saying this is the case, I’m just saying the percentage thing makes no sense to me.) Or am I confused about what they were stating? I just read one article.

    1. I think the percentage makes more sense if you’re not over-eating, just eating to satiety and not until actually full.
      Because the same tinkering of macronutrient intake to tweak the percentage could also be applied to carbs. You could increase your carb intake beyond the general recommendation here of 150g a day to a higher level, say 300g and then just eat twice as much fat and protein to keep the percentage the same but chances are you’re still eating too many carbs, which I’m guessing is even worse if you’re getting extra calories from another source too.

  19. I think you could have just put this in a blog post: “This study is not scientific. It is garbage. End of story.” I mean seriously. How can this be used to make any conclusions: “Nutrient intake data are based on reports of food and beverage intake during a 24 hr period.”? We’ll pay attention when you have some randomized controlled trials of 1000’s of people over more than a 6 month period.

  20. Didn’t the high protein diet group already have a higher association with diabetes than the two other groups? Seems like this would skew the diabetes-related mortality numbers. Unless maybe the numbers were worked in a way to factor out those without pre-existing diabetes.

  21. “Don’t eat a diet of casein, methionine, soybean oil, corn starch, and sucrose, especially if you have cancer.”

    Game. Set. Match.

  22. From the study text:

    “On average, subjects consumed 1,823 calories…” Shouldn’t this by itself have been a red flag that the nutrition data were unlikely to be correct? Bizarre.

  23. So, while the focus has been on protein intake, there’s been zero mention about vegetable intake. Those things have been known to do incredible things. Like prevent the angiogenesis (creation of blood vessels that supply cancer tumors) that leads to rapid growth and proliferation (a.k.a. metastasis) of the cancer cells. Nevermind that maybe eating some veggies with your protein might actually help you all around. It’s never about balance, is it?

    1. I had the exact same thought. I eat mountains of fresh vegetables every day. I basically eat the same amount of protein I’ve always eaten, but since converting to Primal, I’ve replaced grains and simple sugars with fresh vegetables. Since vegetables have almost no calories, under this shoddy analysis, my diet will always be considered “high protein” no matter how moderate my meat intake is. Meanwhile, someone eating a massive amount of protein with lots of grains and sugars may have the same percentage of protein in their diet. Prior to reading this article, I was convinced sugar encourages cancer. Given the high carb content of this study, I remain convinced of that. Grok on!

  24. Not only all this, but echoing the point about the “meat” in this study being industrial CAFO-type meat, people in these age groups have also had different diets depending on when they grew up. In other words, this study takes no account of what people ate for their FIRST 50 or 65 years or whatever. Because, ya know, that doesn’t matter, right?

    The oldest people in this study are actually the most likely to have grown up the healthiest, before the food industry really messed things up.

  25. While checking out the link to “the most recent meta-analysis dealing with diet and diabetes”, I noticed that “the largest effect size” with regard to both improvement in glycemic control and weight loss was seen in the Mediterranean diet, not the low-carbohydrate diet – the plot thickens…

  26. I’m so glad for MDA! I read this and freaked a little too. But I guess that’s what they wanted; to freak people out, to get their story, to create that “buzz”. I’m newly re-dedicated to Primal/Paleo, and I will admit that I got derailed a bit, by all the buzz from Forks Over Knives, until I started to do my own research. You just CANNOT believe all “scientific” studies until you truly dissect the methodology of research. That’s the lesson learned here–again. Thanks Mark!

  27. Hi Mark – super stuff you’re doing with your blog – and I love your interviews online, good man! Now, down to business: the authors of the report failed to include their supplemental data, and I believe it speaks volumes – in short this Study is far worse than the average epidemiological twaddle. It seems that it’s not just poor in the claims made without proper causation being proved – they should have known from their own baseline data that their conclusions were effectively impossible to claim. See my brief analysis below, would love to get your opinion specifically on these aspects:

    Thanks again

  28. Less Biased Conclusion: Not eating a variety of animal proteins could reduce the benefits of higher protein diets.

  29. Thanks for the excellent breakdown, Mark. And for the gelatin tip. I’ve had a really hard time getting to the bone broth making, even with lots of good intentions.

  30. I get a sense that a good portion of this forum is in the over 35 crowd and along with myself at 56 years of age have subjected ourselves to various diet regimens and have found the paleo style of diet and lifestyle to be as good as it gets. Our blood work, waistline, strength, and vitality have improved. We have that “vigor” we want in our lifestyle. That being said, there are many out there who lead a much more seditary lifestyle with a limited caloric intake who life long lives and are also living gracefully. Many people on the sideline see that lifestyle and tout it’s benefits. The Japanese consume 2600 calories per day compared to 3800 calories for Americans and live 4 more years. I believe I can get to their 4 years and go another 4 with VIGOR!

  31. I remember reading something a while back that, if I recall correctly, explained how various groups like the Inuit understood that eating extremely high amounts of lean muscle tissue without any fat in the diet would eventually prove fatal due to the imbalance of protien to fat ratio (hence their preference for fatty meat from marine life). It seems pretty obvious that only eating a specific type of one nutrient and eating it in a high amount would obviously be detrimental to one’s health. Especially if you’re a mouse and that “nutrient” is casein.

    I liken it to backwards grapefruit diet logic: if you eat nothing but grapefruit you will likely get sick and eventually die…but that doesn’t mean that grapefruit was what killed you.

  32. I stopped reading any studies that made the “news” a long time ago. If it’s on the “wire” that means someone paid to put it there through a press release. And… what are press releases for? To get attention for yourself so you can try to make hay/money out of it. Integrity? Pretty much zero. Usefulness? Ditto. Truth? Don’t even ask. News? Mainly a mix of attention-grabbing murders and crimes, attention-grabbing video and most-titillating headlines off the PR wire. TV News? All of the above read by an attention-grabbing barbie-doll in tight clothing. The end.

  33. I used to eat bread, but for the last 12 months I’ve been Primal – Now the clutch has gone on my car! So that’s conclusive proof that the Paleo diet causes premature clutch failure in French cars over 7 years old!

  34. Typically when sourced appropriately (real food) it is very hard to eat “too much” protein. It is when people start dipping into too many liquid meals or processed junk that they can consume before they have feedback loops properly engage.

  35. There are too many publications, and too little good research.

    Randomly asking people what they ate on a single day is ridiculous.

    As a starting point in hundreds of design flaws, is it possible that what food you desire is reflective of your health, instead of causative? Do people who eat more of food X “get sick” more because food X is bad, or because having an illness or genetic makeup makes them crave food X. Pregnant women often crave particular foods, and eat more of them, but we don’t assume that food is what made them pregnant.

    The right way to do a nutritional study would be to assign people to a diet, and carefully follow and monitor them. Yes, that’s complicated and expensive, and might be hard to accomplish without paying subjects, using prisoners, etc., but it would better (and cheaper in the long run) to have a few good studies that mean something, instead of thousands of bad studies. The metastudies don’t mean anything if all of the individual studies had similar systematic and serious flaws. If twenty different people measure sometimes ten times each with the same badly biased tape measure, the overall average will be roughly as inaccurate as an individual measurement.

    Another universal flaw is the failure to sequence the DNA of all subjects. “Some people” will always do better or worse on particular diets, and I suspect the difference isn’t random. It’s important to know why the people who faired better of worse did so, and DNA is a good starting point there.

    Of course, there’s always the use of weight and BMI in dietary studies, instead of actually doing a DEXA scan and getting a more accurate measure of body type and changes.

    Stop Random Acts of “Research”!

  36. “How valid is the dietary data? It was gathered by calling people on the phone and asking them what they’d eaten the previous day and whether that was typical of their normal diet. Seems awfully unreliable and prone to human error.”

    Me, I’m one of those people that can’t remember what they ate yesterday.

  37. Thanks for the summary Marc, but I think this study is even worse than you make out (maybe a lot worse). If anyone’s interested, their supplementary data is here

    When I read the actual paper I thought my head was going to explode – so much of the paper seems to refute the conclusions, it’s unbelievable. I could write an essay on it, but here are the real howlers for me:

    1) The results show that if you eat a low protein diet (L), you are MORE likely than medium (M) or high (H) to die early of all causes, cancer, CVD – everything except … diabetes? Isn’t this the opposite of the news headlines? They also purport to show that the hazard ratio for dying of a diabetes-related condition for H compared to L is in the range 4-1200. Yup that’s right – I’m surprised they didn’t headline with “MEAT MAKES YOU 1200x MORE LIKELY TO DIE OF DIABETES” … with a footnote in tiny font “…but less likely to die overall”. I’ll take those odds.

    2) For cancer death specifically – your lowest cancer mortality is associated with the H group. Where is the headline that says “EATING MORE MEAT IS PROTECTIVE AGAINST CANCER!”? (L-9.8, M-10.1, H-9.0)

    3) In terms of their age bracketing – the methodology isn’t completely clear, but what it clear is the data that they report. For the 50-65 age group, they report 15 hazard ratios which try to link protein and IGF1 with more cancer,cvd,etc. The problem for this subgroup is that 14 of the 15 HRs have p-values of >0.1 (some in excess of 0.8!). For non-scientists, this means this data shouldn’t even be reportable. It’s not science, it’s opinion. Actually it’s worse – it’s marketing.

    4) The low protein cohort looks odd. These people eat the most, are the leanest, have significantly more pre-existing cancer, worse memories and a tiny fraction of the diabetes incidence of the other groups. Also they’re a small portion of the overall study (<7%). It would be REALLY interesting to see the selection criteria for this group – if you forced me to take I guess, I'd say a lacto-vegetarian, cancer-survivors running club, but who knows?

    5) H/T to Jason Cholewa for discovering that the lead author, Longo, is founder of a company called L-Nutra that sells plant-protein supplements for fasting support. Conflict, anyone?

    Personally (although hard to say without data) I think what’s happening here is that the protein study is confounded by diabetes. There’s much higher diabetes in the M & H groups than L (400 & 600% ish). But hopefully we’re not about to hear that you should supplement your CW low-fat diabetes diet with minus-protein, and just eat bread! Funny thing about uncontrolled diabetics – they’re awash in insulin and glucose. And obviously if you’re a cancer cell nothing’s more delicious than a constant sugary bath. Probably they have some protein metabolism issues as well, but the root cause of their condition (and the cancer that often follows) might be much better addressed by eating more fat, less glycaemic carbs, doing some IF and HIIT.

    What’s really interesting is why the diabetes association is there. Don’t know, but the data on the L group MIGHT indicate: more previous medical interventions, more vegetarianism, better “proactive” health management, and [looks to me anyway] definitely more exercise.

    Caveat – 20% protein on a 2400 kcal diet isn’t really that much. It’s 120g protein content, so a good sized steak would do it. And probably it’s ~0.7g/pound which doesn’t seem crazy. I don’t think the study’s a reason to eat a kilo of beef a day, but neither to cut it out.

    Anyway, all in all, the worst example of “science” I’ve seen. Boo. Boo.

  38. Thanks Mark for your comments on this recent study.
    My simple take is that I need to balance protein with fats and plenty of vegies. No change there.
    And, be as active as possible. No change there.

  39. The study was torn apart pretty much but it got huge media coverage with it’s sensationalistic headline ‘more dangerous than smoking’

    Dr John Briffa did a great piece

    and before him Zoe Harcombe

    It got people talking. That’s for sure. I eat a lot of protein, but i also eat lots of vegetables and the food sources are clean and unprocessed…..BUT do I smoke, do I work out – what’s the control group etc?

  40. Didn’t take any notice of this article when it first came out. Setting aside smoking, alcohol etc. I firmly believe that the way we work has a greater impact (long term) on our health than eating meat – by that I mean sitting behind a screen at work and then sitting behind another screen when we get home (TV, iPad, phone).
    Agree with Mark on vigour – just taken up boxing at the age of 63 and can’t believe the level of stamina I seem to have.
    When I read that the likes of Sir Steve Redgrave (UK 6 times Olympic gold medallist – rowing) and Sir Ranulph Fiennes (worlds best known explorer – Everest, North Pole) both suffer from Type II because of all the chocolate, cakes and biscuits they’ve wolfed down over the years I think I’ll take the risk with meat

  41. Again it’s been proved that one need to eat balanced diet, eating protein or vitamins excessively can negatively affect your health. So always focus on eating all nutrients.

  42. I was vegan (I know, I know) for a few months and I felt so awful! My doctor finally told me to start eating meat again because I had no energy whatsoever. Just thought I would share how eating more protein has made me feel healthy.

  43. “Don’t eat a diet of casein, methionine, soybean oil, corn starch, and sucrose, especially if you have cancer.”

    Sage advice right there. Nice work Mark.

  44. A lot of these “studies” that are popping up are reaching. Since industrialization and with the growing affluence of the west, people have been looking for validation in taking the easy way out, and getting more unhealthy because of it. Being properly healthy takes a lot of hard work, discipline and commitment. Naturally, folks will try and justify why working hard, being disciplined and committed are not the way to go.

    I’ll take my chances on rate of tumor growth at 65. They can have their COPD, CVD, Diabetes, Acne, IBS, and Gout.

  45. nice work Mark and everyone for commenting and exposing this so-called study. i would only add a potential conflict of interest issue that hasn’t been raised by others. namely, four of the paper’s authors are research team leaders or sit on the board of advisors of a company called l-nutra, see

    from their website, they seem extol the benefits of fasting, which is fine enough, but are also developing supplements aimed at obese or recovering patients. they don’t give a lot of details about the make up of the products, but the description of one of them, prolon, is telling ( L-Nutra has developed ProLon™2, which is a proprietary all natural product produced from vegetables (not animals) to achieve a source of all the important vitamins, minerals and other essential micronutrients provided in a balanced form that optimizes absorption and nourishment as a highly nutrition diet would achieve… Prolon™1 and 2 are proprietary, solely plant-based products, comprised of vegetable medleys, broths, energy drinks, teas, and nutrition bars

  46. Yes they are right! A high protein diet is far deadlier than smoking as it requires far more cows to die to sustain the diet! 😉

    1. Well, the cows are not smoking so being a protein source would prove to more deadly than smoking for them. 😉

      1. Yeap, that is what I meant! But in essence if you look purely at the conclusion, the protein diet is deadlier than smoking so they are right. (The fact that is deadlier for the cows is just a “minor detail” for the researchers! 😉 )

        1. I wonder what the next step in improving cow farming is.. giving them pasteurized skim milk?

  47. Thanks for clearing the air about this study, it is pretty amazing to see so many people go crazy about different studies and then to find out how they get their info! I don’t really get how a study can expect to be taken really serious with such unreliable sources of information. Asking someone what they ate yesterday? They might as well as what I ate last year, because I will never remember!

  48. Surely this study says that middle-age people should eat MORE protein?

    It says that there is a relationship between the protein that you ate 18 years ago and your current health. If you are 50-65, the ‘effect’ of protein is bad, if you are 65+ the effect is good.

    Most people have taken away from this that people should eat less protein during middle age (ie 50-65). But surely people should start eating more protein 18 years before they hit 65, ie from age 47… ?

  49. Also quite interesting, the main author of this study, Valter Longo:

    “The study claims to have adjusted for protein in general vs. animal protein to conclude that animal protein is the harmful factor and not protein per se. Call me suspicious, but I always check for conflicts of interest and the lead researcher, Dr Longo, has declared interests in (actually, he’s the founder of) L-Nutra – a company that makes ProLon™ – an entirely plant based meal replacement product.”

  50. The Mongols being nomads had a red-meat based diet with hardly any vegetables and they managed to conquer 5/6 of then known world. It’s got tell us something.

  51. I believe factory, feed lot beef and cured deli meats were included in the studies. That seems to be the case when there are studies undertaken regarding protein. In some peoples eyes (research included) all meats are lumped together under the heading of protein when the difference and benefits of grass fed and finished proteins are a night and day difference.

    You can clearly benefit by moving away from refined carbs, sugars and starch to more protein centered but then move all the way to grass fed and finished proteins to complete the transition.

  52. Hi folks. Don’t waste your time with this rubbish made just to sell papers

  53. Achieving a protein intake of 4-7% of calories would be difficult on even a vegan diet. Even a vegan diet will typically provide about 10% or more of calories from protein, unless it consists almost exclusively of vegetables, fruits, and nuts and almost eliminates grains and legumes.

  54. My question is if you are over 50 and all your health markers indicate no problems (lipid profile, CBC, etc…) isn’t that better data than an epidemiological study on age related cohorts? To take it one step further, if your numbers were borderline before subscribing to a “lifestyle” and the numbers got better using it (high carb, low carb I don’t care what diet) wouldn’t it make sense to stay on that course?

    In the engineering field where I work, the general rule of thumb is that specific localized data overrules standardized data. The best data is site specific. So, personally I will continue on my modified Primal lifestyle until I see evidence that MY situation needs to change through quality of life or medical blood work.

  55. Mark,

    Could you tell us which parts of the animal are highest in glycine?