Meet Mark

Let me introduce myself. My name is Mark Sisson. I’m 63 years young. I live and work in Malibu, California. In a past life I was a professional marathoner and triathlete. Now my life goal is to help 100 million people get healthy. I started this blog in 2006 to empower people to take full responsibility for their own health and enjoyment of life by investigating, discussing, and critically rethinking everything we’ve assumed to be true about health and wellness...

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August 17 2015

Dear Mark: Low-Fat Versus Low-Carb Study and Plain Ol’ Olive Oil

By Mark Sisson

For today’s edition of Dear Mark, I’m answering two questions from readers. First, I field one of the dozens of emails I received concerning the latest low-carb versus low-fat study making the media rounds. The reports have ranged from declarations of low-carb dieting’s imminent death to more reasonable discussions of the actual paper. The Time article actually keeps things closer to the latter, which was nice. For the final question, I discuss the merits of regular old olive oil. Is extra virgin olive oil the only one worth entertaining?

Let’s go:

Hi Mark,

Apparently low fat trumps low carb. Here’s the time magazine link.

Here’s the full study.

Now the authors DID say not to jump to conclusions. I still am not sure their “fats” were not crisco, margarine, or any other trans fats.

Look forward to the post :).

Best wishes,


Thanks for the link, Anand. Yeah, this is a popular one. It’s all over the media and yours was one of dozens of emails asking for my take on it. So I decided to take a look at the full text (PDF).

Here’s how it went down:

A group of 19 overweight adults (10 men, 9 women) went on a “starter diet” consisting of 50% carbs, 35% fat, 15% protein for 5 days. After the starter diet, they reduced calories by 30% for six days. The low-carb arm dropped calories by reducing carbs and keeping fat and protein constant. The low-fat arm dropped calories by reducing fat and keeping carbs and protein constant. Everyone tried both low-fat and low-carb diets with several weeks in between to “reset.” Researchers tracked biomarkers, body composition, body weight, energy expenditure, and the composition of that expenditure throughout the various arms. What did they report?

During the low-carb arm, subjects lost more weight and burned less fat. The low-fat arm lost slightly less weight but burned more fat. This was determined by measuring something called “cumulative fat imbalance,” calculated using fat intake and the amount of fat metabolites in participants’ breath.

Should we ditch low-carb and adopt low-fat diets? I’ll give a few random thoughts on the paper in no particular order and you can decide:

Six days isn’t very long. Fat adaptation takes upwards of several weeks to really get going in some folks, especially if they’re coming off the carb-heavy “starting diet” of 50% carbs, 35% fat, and 15% protein. I realize that doing a full-on metabolic ward study with humans is expensive, and they did a great job with this one, but I would like to see the same study extended for several weeks or even months to allow for full fat adaptation. Fat chance of that happening, though.

Free-living people don’t reside in metabolic wards where the caloric content of their meals is objectively determined by an outside party. This study wasn’t trying to determine which diet works best for fat loss, and the lead author even admits that the results don’t mean much for people trying to lose weight. But beware of the media breathlessly reporting the death of low-carb fad diets based on this study. Free-living studies, where people spontaneously determine their own caloric intake, usually find that low-carb diets work better and tend to cause greater reductions in calories than low-fat diets. Low-fat diets work if you’re really committed and/or there’s someone making your meals and preventing you from eating anything else. Also helps if you’re insulin sensitive.

These were pretty healthy overweight people. They had great lipid numbers, low triglycerides (for their weight), good TG/HDL ratios, and relatively low fasting insulin levels, indicative of good metabolic health and insulin sensitivity. What about when the subjects are obese and hyperinsulinemic? Low-carb diets lead to greater weight loss in those folks.

Sure enough, the men were more insulin sensitive and experienced greater weight loss than the women, who tended toward insulin resistance. It’s well known that insulin resistant patients lose more weight on restricted carb diets, while insulin sensitive patients can get away with higher carb intakes and often lose more weight on low-fat diets.

The low-fat arm of the study was very low-fat: 8% of calories from fat. The low-carb arm was rather moderate: 29% of calories from carbs. Moderate carb diets seem to work really well for weight maintenance, but not so great for the kind of rapid fat loss people expect from low-carb diets. Indeed, in the discussion section of the paper, the authors speculate that fat loss during the low-carb arm would have outpaced the low-fat arm were the former more severe in its reduction of carbohydrate. I—and many others—find that severe carbohydrate restriction is easier to achieve than severe fat restriction in free-living situations, AKA real life.

This was not a ketogenic or VLC diet study, nor was it trying to be. And that’s okay. As the authors say:

Given the composition of the baseline diet, it was not possible to design an isocaloric very low-carbohydrate diet without also adding fat or protein. We decided against such an approach due to the difficulty in attributing any observed effects of the diet to the reduction in carbohydrate as opposed to the addition of fat or protein.

Low-carb diets deplete glycogen first, then fat. The low-fat arm burned 2000 more fat calories than the low-carb arm, yet the difference in energy expenditure was only 300 calories. What gives? Since the researchers speculated the low-carb arm lost a ton of water weight, this indicates that they were tapping into and burning their glycogen stores (glycogen comes bound with water so burning the former depletes the latter, too) for energy before utilizing the fat stores. Why burn body fat when there’s quick burning glycogen available, you’ve just come off a high-carb starter diet, and your body “expects” glucose? Had the study been extended, I suspect the low-carbers would have burned through their glycogen stores and increased the rate of fat burning.

Despite the claims to the contrary, the researchers only showed increased body fat loss via measurement of breath metabolites. They weren’t actually able to confirm a significant difference in body fat between the two arms. They even used DXA, the gold standard for detecting shifts in body composition, and came up empty.

All that said, this is an interesting and well-done study — just not enough to justify dismissing low-carb.

Dear Mark,

I recently bought a bottle of Extra Virgin Olive Oil for about $8.99, and yes I know it’s too good to be true. But after tasting, and then researching (insert brand name here), I realised that the olive oil I purchased wasn’t extra virgin BUT it was still 100% olive oil. So my question is; is cooking with a blend of different grades of olive oil (rather then just extra virgin) still primal?


Yep, it’s still a pretty good oil. The omega-6 content remains low and the MUFA content remains high.

All that’s missing is the flavor and the unique olive polyphenols. Those are big misses, to be sure, as the polyphenols found in extra virgin olive oil imbue it with antioxidant effects, make the oil more resistant to heat damage, and offer cardio-protective health effects. But refined olive oil is probably better than most other oils for heating. In one study, the authors heated various oils to “deep-frying conditions” and checked oxidative markers every three hours. The olive oils made it 24-27 hours of constant high heating before reaching the maximum legal value of heat damage. Not bad, and it’s not like you’re going to use the same pot of olive oil to deep fry for a full day anyway.

As for in vivo oxidation? Whereas EVOO consumption reduces LDL oxidation, consuming refined olive oil has no effect in either direction. It’s not “bad.” It’s just not all that great, either. “Neutral” is a better description.

Keep it around for sautéing or even the odd deep-fry session, but definitely go out and find a quality extra virgin olive oil. Believe it or not, quality EVOO exists at that price point. If you have a Trader Joe’s nearby, grab their California Estate EVOO for $6 or $7; it’s probably my favorite “cheap” one.

That’s it for today, everyone. I’d love to hear your thoughts on the low-fat/low-carb study down below, plus any input you have concerning regular old olive oil.

Thanks for reading!

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49 thoughts on “Dear Mark: Low-Fat Versus Low-Carb Study and Plain Ol’ Olive Oil”

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  1. Interesting info on Olive oil / EVOO and heating. I thought heating olive oil was a big no no because it turned it to trans fat? Maybe I misread somewhere…

    1. A quick online search says EVOO is actually quite stable as oils go and can safely be used for frying. It does not turn into trans fat with normal home use. However, overheating olive oil (or any oil, for that matter) can degrade it. Personally, I would keep it below its smoking point, and I wouldn’t deep-fry with it.

  2. My question is why do all these studies set up low-carb to fail…always. I mean how to do low-carb is pretty much common knowledge these days (50g-100g/day), yet every time they do a study of “LOW CARB” the diet has at least 2x to 3x that amount. What are they afraid they will find out? Even though today I lean more towards resistant starch, I just hate to see biased crap pushed out as “SCIENCE!” All we can do is keep fighting the good fight and pointing out the fact that the emperor is naked(and does not look good).

    1. So true. Your comment about the emperor should make the comment of the week!

    2. Because you and Mark misunderstand the design of the study. The study is looking at Gary Taubes’ claim that you have to reduce carbs to lose fat. They showed in the study that yes, indeed you can lose weight without reducing your carb intake. They did it with a metabolic ward study so that there is no question about that intake.

      This study is not designed to answer whether you can lose more weight with one diet vs. the other, have an easier time maintaining weight loss, etc. This study doesn’t try to give you the answers to these questions, so there’s no point looking for them.

      The take away from this study is that you can lose fat while eating a diet that is relatively high in carbs. Thermodynamics (CICO) wins again.

      1. This is an excellent point! The real way that the low-carb diet wins is sustainability. If everyone lived in “lab conditions” no one would be overweight. But when we’re forced to make dozens of decisions every day about our food choices, it’s very important that we are able to make the right ones. Our hormones are more powerful than our willpower and will eventually win out if we are in a state that our body interprets as deprivation.

      2. I disagree that CICO wins again. That may be true in insulin sensitive people, or even for an initial 2-3 weeks, but I was a champion low fat dieter for years, and after 5-10 pounds of weight loss, I could lose no more, even on what I called the “no fat” diet while eating under 1000 calories per day (1200 and I would be gaining). On low carb, 20+ pounds disappeared in 5 pound increments over a 6-8 month period and has been easy to maintin for 3+ years. I conclude the study has little interesting to say about real world conditions for people trying to reach and maintain lower weights.

        1. CICO is totally wrong on principle. Humans are not nuclear powered. We cannot convert fat ,which is matter, into energy,nor heat. Totally wro g fitness industry jun k……

          Kriger,Colpo.McDonald are all science illiterate.

      3. The researchers specifically claim that their research disproves “the theory about metabolism that has previously been used to recommend low-carb diets”. However, none of their subjects were actually on a low-carb diet. Your assertions are therefore wrong, and their study is broken.

        1. Very good point, 29% carbs would, on a VERY low-cal (1200cals a day) diet still be 87g carbs a day, and I strongly doubt the daily calories were that low. That’s still way above Atkins, especially the older versions of that plan.

          At 1500cals, we’re looking at 108g, at 200cals / day, 145g… so no, this definitely was NOT a low-carb diet.

        2. ^ Last figure there is missing a zero, I meant “at 2000cals / day, 145g.”

        3. I just found the actual figures – they started at 2700cals / day.

          They cut this by 30%, that’s 1890cals.

          29% of 1890cals total is 548.1cals from carbs.

          At 4cals/gram, that’s 137g carbs a day.

          That was this study’s “low carb diet”?


      4. “CICO wins again”…. of course it does, it is a law after all, when has it ever “lost”??

        1. First, it is Not a law. IT IS A THEORY..A MODEL …A principle. The laws of thermodynamics are Not laws as in societal sense. That is NOT A what a law is in Science.

          And CICO is literally NOTHING. It is moronic fitness industry speak.

        2. CICO is literally a laughable nothing expression from moronic fitness industry. Matter does Not get converted into energy heat in a human……

          There is No physical way for CICO to be true …im any way. Wrong principle from start…..

      5. You are not science literate. There are six conservation principles. Humans are NOT nuclear powered. We CANNOT convert fat into energy. We do NOT convert matter into energy. There is NO caloric energy being turned into matter either in a human. Stop misusing science and mixing up Einstein’s work of mass energy equivalence in a way he would not forgive.

        P.S. All metabolic ward means is IN A HOSPITAL. CHEATING could have HAPPENED. Those fancy Internet guru speak is not at all a guarantee of patients not deciding to cheat. BOTH low carb AND CICO are WRONG.

      6. Again, NO caloric energy is being converted into matter in a human. We are NOT nuclear powered.

        Energy is nothing material. CICO pro vides NO PLAUSIBLE MECHANISM WHATSOEVER as to how fat could be shed from body. We do Not convert matter into energy.Stop abusg science. McDonald and Colpo are not scientifically literate at all.

    3. Great question, Chad. I question who paid for the research? Was it Kraft, or General Mills, or Nabisco? You get my drift……

  3. I know that olive oil is not healthy simply because the Canada food guide says it is healthy and they have everything else wrong.

    1. I’m surprised the rapeseed growers let them say olive oil is healthy. Rapeseed is not an appealing market name so they renamed hybrid lower acid Canadian seed oil, Canola oil. Supporting olive oil over a major export crop is not good for business. Aye?

      1. It’s convenient to hide behind – “Olive Oil Mayo” – yum, super healthy!

        Label shows 5% olive oil, the rest canola.

        1. Hey, the marketeers do the same with whole wheat bread, so why not with mayo?

          Thing is there aren’t enough masochists to make a market for real honest whole wheat bread, plus it does not keep well enough for our food distribution system.

  4. Sunstainability is definitely key in the real world! I also think reports of improved health; even those as simple as less airborne allergies also goes a long way as well:)
    Recently, my husband and I, somewhat accidentally, did our own “study” of eating styles. We happened to attend a paleo dinner hosted by an organic farm. I can’t remember the number of people, but it was at least fifty. On the way there, we were joking about how we expected all the people to “look fit”. Well, they did! Old and young everyone looked trim and healthy. A few weeks later we attended a dinner sponsored by a local CSA with all farm grown ingredients . These were basically health conscious folks, most of them the farmers or the CSA participants (and about the same number of people as the previous dinner). We were now curious as to how they would stack up? Well, they were about 50/50. Now, take this one step further and take a look at 50 random people in a mall food court; maybe 1/4 of the folks are now looking fit and trim depending on where you live. It may not be a scientific study and there were no controls of any kind but it was an interesting view of eating in the real world!

    1. The comparison of the two dinners is interesting. I think extending it to the food court at the mall runs into issues of income, though. Perhaps at a very upscale mall, you’d get the same socio-economic status folks as the ones who can go to dinners at paleo and organic farms? Otherwise, issues of class and money and availability of healthy options become pretty prevalent (for example,

      1. I saw a lady with her three children, aged from about 8 to 15, in the supermarket last week and she had not one fresh food item in her trolley.
        No fresh food at all.
        It was all frozen packaged crumbed or battered fish, hamburgers, chicken, apple pies and ice cream. Sweet biscuits, cakes, pasta with big tubs of commercially made sauce, big bags of potato chips – you get the drift!
        Not even one piece of fresh fruit or a vegetable in sight.
        She did have a big container of fresh milk, chocolate I think, along with a big box of a flavoured sugary cereal.
        By the look (and sound) of the family I would have thought lower socio economic and not well educated but the total at the end of her shop was quite large. It’s not cheap to buy everything pre packaged and prepared.
        Sad to see the kids ripping into the potato chips before mum even got out of the store.

        1. maybe she does her fresh food shopping at farmers markets. People could jump to similar conclusions about my diet when I’m shopping in a supermarket. Well, not that similar. It would be more like: cheese, cream, milk, cheese, butter, cheese, yoghurt… and toilet paper. That’s what supermarkets are good for!

    2. Really interesting observation! While I personally believe eating a Paleo-influenced diet will keep you relatively fit regardless of your exercise level, I’m willing to bet the paleo dinner crowded was more fitness oriented. What would be interesting is if you had polled each group on their fitness habit. Guarantee the paleo group does more strength training and the CSA group more cardio. We should host our own dinners and find out! At the very least, we get two delicious dinners 😉

  5. Great points- I had written this study off because of the short duration and because the low carb group was really more of a watered down zone diet, but I didn’t consider the insulin sensitivity issue.

    What do you think about measuring insulin sensitivity by trying different meals, and seeing how you feel after a low-carb vs moderate carb, low-glycemic meal? Do you think how you feel after a meal is a good gauge of the insulin response?

    1. I think I might be doing this all the time instinctively, because I know that I feel much better if I eat low carb, or low glycemic meals. Maintaining proper body weight is all about exercise and food choices, AND, duration and sustainability of both conditions.

    2. The researchers went out of their way to find study participants who were all insulin sensitive. So it doesn’t say much about those of us who are highly insulin resistant.

      And how did we get to be so insulin resistant?

      Eating lots of carbs. So a six day trial doesn’t say much at all about the majority of the obese population of people who are insulin resistant.

  6. I appreciate the knowledge that OO alone, vs EVOO, is still good enough to cook with. On a super tight budget, it’s easy to make that choice if it becomes necessary. I don’t suppose I would have worried too much when faced with the decision, but it’s nice to have some additional information going in!

    As for the study, a short-term trial with relatively few participants; better than just observational, but as Mark points out, could be better with longer duration (and more participants). One person commented above that Mark “missed the point of the study” and that is wasn’t conducted for determining whether or not an individual would lose more weight on a low-carb vs low-fat diet; unless I understood it wrong, I think that’s exactly what the first sentence of the abstract is getting at; that *was* the point of the study.

  7. Here is my take on this, and I did hear about this study about a week ago as they mentioned it on the news. First things first, a couple of weeks is not enough time to measure this type of study. Though it’s a nice start, it isn’t enough time.

    Also, the study went as exactly I would have expected it too.

    Low Carb Arm (Lost more weight but less Fat) – Well yes, they burned off their glycogen stores reducing the water in their system hence the greater weight loss (initially).

    Low Fat Arm (Lost less weight but burned more Fat) – Well yes, the glycogen stores I assumed stayed semi-topped up and so did the water weight, so of course less weight will show to come off while more fat will show to come off (due to lack of water).

    The smoking gun – What was each individuals insulin sensitivity range? Low carb is a longer process where as to turn someone more insulin sensitive so they spend more time in fat burning mode. You can still burn fat, you just burn fat faster when your insulin sensitive, and this is not a quick fix, certainly not in 6 days or 2 weeks time.

    So as Mark said, the group whom is insulin sensitive can get away with higher carb/lower fat diets, while the less insulin sensitive crowd (like me 2 years ago who drank energy drinks regularly) do better on low carb. Now as I type this, I do better on moderate carb on average.

    So going forward, how can researches conduct “accurate” studies? The same way I coach people with their diets, ask them what their goals are, and what their eating patterns are like. Those looking to lose weight, will not follow a diet meant for maintaining, and they certainly won’t be eating like a bodybuilder to gain mass. Those looking to gain weight, certainly won’t be taking a low-carb approach.

    If the researchers are working with people whom have a history that points to insulin resistance (again like I did 2 years ago with all the energy drinks I drank), then take a group like me and put them on low-carb and high carb and derive your results from there. If they are going to get someone whose history suggests their insulin sensitivity is moderate, then conduct the study on people whom are in the same boat. It’s all relative, but don’t mix people together whom have higher and lower insulin sensitivity levels.

    The “me” of today does considerably different on a high-carb/low fat diet than it would have done 2 years ago.

  8. I’m curious whether anyone who thinks calories in, calories out (CICO) is for real, thinks anyone would lose weight if the 137g a day I estimated above that the “low carb” dieters on this study ate, had been from sugar alone? Let’s say, some proteins and fats, a zero-calorie fibre supplement, and 137g pure table sugar.

    If not – the moment that turns into “Oh but they’d need to be complex carbs” – then a calorie is no longer a calorie, and the whole insulin pathway thing kicks in.

      1. Wrong pri ciple from the start. Humans cannot convert matter into energy,nor heat.there is no mechanism for CICO to be true. None.

  9. Hi Mark,

    I am a producer of (what I believe) is the EVOO on Earth. My family’s square-mile olive tree farm in Greece has been yielding amazing “zero” acidity olive oil for 6+ generations.
    Our Manaki olives make some unbelievable tasting EVOO loaded with antioxidant polyphenols which have helped to pretty much eliminate heart-related disease from our extended family for many years.

    Even though I import my EVOO for sale in the North American market, I have to say that the costs involved in chem-free production, packaging, QA/QC, export/import etc. make it impossible to sell at a “low” price even without middle-men. This fact makes me very suspicious about the quality of many brands out there that somehow have discovered the holly grail of cheap “top quality extra virgin” olive oil. BTW, I give that a 10 on the Alchemy scale.

    I would welcome sending you a sample of my Olive Crate EVOO to try.

  10. kate, please see the link in my name below for a critical examination of this. There are many more, as well.

    Interestingly, the 173g average carbs he took in per day is only 36g over the 137g of the “LOW carb diet” from the study discussed in this post.

  11. Hi Mark,

    I am a producer of (what I believe) is the best EVOO on Earth. My family’s square-mile olive tree farm in Greece has been yielding amazing “zero” acidity olive oil for 6+ generations.
    Our Manaki olives make some unbelievable tasting EVOO loaded with antioxidant polyphenols which have helped to pretty much eliminate heart-related disease from our extended family for many years.

    Even though I import my EVOO for sale in the North American market, I have to say that the costs involved in chem-free production, packaging, QA/QC, export/import etc. make it impossible to sell at a “low” price even without middle-men. This fact makes me very suspicious about the quality of many brands out there that somehow have discovered the holly grail of cheap “top quality extra virgin” olive oil. BTW, I give that a 10 on the Alchemy scale.

    I would welcome sending you a sample of my Olive Crate EVOO to try.

    1. I’m in the UK and supermarkets here sell “standard” olive oil and EVOO at the same price, £3.50 per litre (about $5.50). How are they able to do it so cheaply, and is there actually a difference between standard and EVOO? For comparison, organic is £5 per litre (~$8).

  12. “All that’s missing is the flavor and the unique olive polyphenols. Those are big misses, to be sure, as the polyphenols found in extra virgin olive oil imbue it with antioxidant effects, make the oil more resistant to heat damage…”

    That’s interesting.

    I have an olive oil at home where on the label it says exactly the opposite.

    It’s called “Frying Oil Olive, for high temperatures” which is olive oil that has undergone refining. The refining process supposedly makes the oil more resistant to temperatures than extra virgin olive oil.

    Now I’m a bit confused who is right here.

  13. Mark,
    The researchers weren’t statistically powered to detect significant effects using DXA, and they were very up front about that. Your statement, “came up empty” is tremendously misleading. What this article effectively did, by showing reductions in insulin in the reduced carb group versus reduced fat group (note, they used the term “reduced” and not “low”) was that fat loss does not require the insulin changes that Gary Taubes asserts. If you haven’t already, check out Stephan’s post about this. Kevin’s been really reasonable in presenting these findings. Regarding your suspicion (“low-carbers would have burned through their glycogen stores and increased the rate of fat burning”) — per some simple calculations, the reduced carb arm did burn through their glycogen within these 6 days – not sure there’s reason to believe that 6 days wasn’t enough to burn through it, and the predictive mathematical model didn’t show an increased rate of fat burning relative to reduced fat, if I’m remembering correctly. Also, keep in mind that although this wasn’t low carb per se, this was likely a massive reduction in carbohydrate compared to the pre-intervention carbohydrate intakes, given the pre-intervention caloric intakes needed to achieve and maintain the adiposity that participants began with. I think Kevin was really reasonable about the conclusions he drew here. Again, I think Stephan hit this one on the mark.

    That said, I do think that Paleolithic are likely more satiating, which is critical for anyone looking to reduce body fat. Feeling hungry all the time is a recipe for weight gain. We’re currently studying a Paleo Diet (vs. Mediterranean diet) here at UCSF among women with PCOS and will be able to speak to this sort of question at the study’s conclusion. It’s too bad Kevin didn’t throw in a measure of hunger / satiety (or report on one, if he did in fact assess it).

    Best, Ashley

  14. Yes, I am Razwell, and I just handed Anthony Colpo his butt publicly. CICO is totally wrong from the start. Humans CANNOT CONVERT MATTER INTO ENERGY. CONFRONT KRIEGER,COLPO AND THE REST.