Dear Mark: Red Meat and Breast Cancer, Net Carbs, and Solutions for Excess, Unavoidable Sun

Processed Red MeatFor today’s Dear Mark, we’ve got a three-parter. First up, I discuss the latest study claiming that red meat will kill us all. Or maybe it’ll be killing roughly half of us all, seeing as how this paper concerns red meat and women’s breast cancer risk. Next, I give my position on the “net carbs” issue. Do we subtract fiber, leave it as is, or do something else entirely? And finally, I talk a lot about the importance of getting enough sunlight. But what happens when getting enough sun isn’t the problem? What can an outdoor worker do about too much sun?

Let’s go:

Hi Mark,

I would love to hear your take on the new study claiming that red meat raises women’s breast cancer risk. This has been all over the news without any dissuasion of other variables such as: it was a “recall” study where subjects were asked what they ate over the past 20 years, was there a category distinguishing McDonald’s cheeseburgers vs. grass fed filet, were the participants who remembered eating less red meat consistently active, how did the subjects obesity levels factor into the results, etc. It seems that this is a big leap to take in a study based on memory of what nurses ate. Thanks!

K. Hunter

Oh look, Walter Willett has authored another study condemning red meat. I’ll always respect and admire his voluminous mustache, but I don’t think much of this latest paper. You point out a lot of shortcomings in your question. Yes, it was a recall study. No, they didn’t distinguish between fast food burgers and pastured steak. They didn’t control for activity levels (which definitely affect the risk of getting breast cancer), though they did for obesity. The biggest thing that jumps out is that they didn’t separate unprocessed red meat from processed red meat. From the Methods section:

Total red meat items listed on the food frequency questionnaire included unprocessed red meat (beef, pork, or lamb as a sandwich, pork as a main dish, beef or lamb as a main dish, and hamburger) and processed red meat (hot dogs, bacon, and other processed meat such as sausage, salami, bologna).

That’s pretty unforgivable, and if you stopped reading now to go eat a beef shank, I wouldn’t blame you. Confounding processed and unprocessed red meat means that a nurse who brought in leftover osso buco would be lumped in with the  nurse who ate microwaved Oscar Mayer hot dogs for lunch everyday. Does anyone really think that hot dogs and braised veal have the same effect on breast cancer risk? Or even a similar effect? “Red meat” is not a monolith. It’s just a term we use to categorize foods that share a few characteristics. This makes discussing foods easier, but our discussions become less precise and any conclusions gleaned from them less meaningful. I don’t blame them, really. Breaking up “red meat” into grain-fed beef, grass-fed and grain-finished beef, grass-fed/finished beef, pastured pork, conventional pork, and so on would produce the most accurate results, but it would make research difficult to conduct.

Such categories may make research easier, but you’re not eating “red meat.” You’re eating from among the thousands of foods that qualify as red meat. And since this study didn’t even distinguish between the most basic sub-categories (processed red meat and unprocessed red meat), it’d be unwise to ascribe it any significance, let alone modify our diet based on its conclusions.

It’s not like this is a novel pursuit, a foray to an untapped reservoir of nutritional epidemiology. It’s old news. People have been looking for evidence that red meat increases the risk of breast cancer for years. By and large, they’ve come up empty. Even looking at the constituents of red meat for evidence of a link hasn’t gone anywhere. Heme iron, the type found abundantly in red meat, is not associated with breast cancer risk. Fried meat is sometimes associated with breast cancer, but other studies have found that a person’s intake of heterocyclic amines, the carcinogens that form when meat is cooked and seared under high heat, has no association (but omega-6 intake seems to be connected). Oh, and how about animal fat? No relationship with breast cancer risk.

Even if this paper was sound and relevant to a healthy Primal eater, we know that many nutrients found in red meat, like conjugated linoleic acid (CLA), are associated with a reduced risk of breast cancer. Another one, carnitine, appears to be protective once a person has breast cancer. I’m not saying that eating steak will cure or prevent breast cancer. That’s not really supported by the evidence, though a few potential mechanisms (CLA, carnitine) look promising. I’m saying that the opposite statement – that red meat increases the risk of breast cancer – has even less support in the literature. It’s the same crazy situation where even though gouda is one of the best sources of vitamin K2, a heart-protective nutrient widely recognized by health experts, they tell heart disease patients to get their vitamin K2 from supplements, not gouda, because “full-fat cheese is bad for your heart.”

So yeah, this paper isn’t groundbreaking, and I don’t think it tells us anything about the effects of eating grass-fed lamb, but it’s still not a very good idea to eat a lot of fried, well-done, and/or processed meat. And make sure you exercise.


I picked up The Primal Blueprint about a year ago, and have been following it ever since. I am not overweight for the first time in my adult life, and feel incredible. I am still struggling to lose the last 10 or so pounds, and get my body fat into a healthier range. I am diligently staying within the 50-100g/day carb range, with a few days here and there of below 50, and seem to be stuck on this plateau. My question is, are you recommending to stay within 50-100g of total carbs, or factor in the fiber and go by net carbs? I have been going by total carbs, which means I’m netting around 40-60 carbs a day (around 60-90 total carbs). I’m not sure if this is my sweet spot, since I can’t seem to get this last bit of weight off, and would love your opinion!


I don’t really do the “net carb” thing. That often leads to micromanagement, which is bad for some people. If you love to micromanage and thrive doing it, have at it.

I find it easier (and more helpful) to think of non-starchy vegetables as “free” than to subtract fiber from total carbohydrate, and it accomplishes similar things. Leafy greens? Broccoli? Bok choy? Summer squash? Zucchini? Cabbage? Eat as much as you want. The carbohydrates are negligible (you probably use more glucose digesting non-starchy vegetables than they contain) and they’re inherently self-limiting. No one is carbing up with a salad bowl full of a couple pounds of steamed kale before a race; it simply wouldn’t work. No one is carb-binging on spinach the way they might binge on roasted potatoes; spinach technically has carbs, but not really. No one is getting fat because they ate too much lettuce unless it’s drowning in dressing; you’d get sick of it before you could consume a significant enough amount of lettuce calories.

The carbs on the Primal Blueprint Carb Curve primarily refer to carbohydrates from starchy vegetables (winter squash, beets, etc), tubers, roots, and fruit.

What’s up, Mark? I just started a new job at a marina. It’s great – I’m outdoors for much of the day, I’m active and moving, and I’m doing something that I love which is working on boats.

Here’s my question: Since I am outdoors much of the day, I’m concerned about getting too much sun. I love getting some sunshine and I know the sun isn’t poisonous, but sometimes I’m out in it for 6 to 7 hours at a time (minus a few breaks here and there).

You usually recommend people head inside or get out of the sun when they feel like they’ve had enough, but that’s not always an option when I’m working. Since summer’s here now, and people are going to be on the lake or at the beach, I’m curious what you would recommend when getting out of the sun isn’t necessarily an option.

Should I use sunscreen? Another alternative? The main goal is just to keep from burning, right?



First off, the fact that you’re moving around all day helps. Rather than laying out and exposing a big uniform slab of flesh to direct sunlight for an extended, unbroken amount of time, your work on the boats has you bending, pulling, crawling, and contorting yourself and exposing different bits of skin to the sun. This is safer than direct protracted exposure. It’s known as “occupational sun exposure,” and it’s usually linked to less skin cancer than intermittent sun exposure.

Second, not burning is a good sign. It’s certainly better than burning, which definitely increases the risk of melanoma. And people with the innate (or cultivated through dietary and other lifestyle measures) ability to tan rather than burn are less likely to develop deadly skin cancer. Despite the conventional wisdom, a light base tan is not a definite indicator of irreparable skin damage. Assuming you go about attaining it the right way – through steady and measured, rather than intermittent sun exposure – it indicates good sun resistance.

However, six or seven hours is still a long time to be out in the sun and sunscreens may be a good bet. Some sunscreens work better (and are less toxic) than others. Zinc oxide – the white, goopy stuff that doesn’t really disappear after application – actually provides a physical, rather than chemical, barrier that protects against both UVA and UVB; most chemical barriers block only UVB, thus preventing the synthesis of vitamin D that helps protect your skin from the UVA. Some of the latest zinc oxide sunscreens are better at blending in, but they’re not perfect. You’ll still give off a faint white sheen (which is better than a burn). Focus on the areas of your body that receive the most direct sun, like your shoulders, neck, nose bridge, and clavicles. The Badger Balm line of zinc oxide sunscreens provides a physical barrier and manages to be somewhat inconspicuous.

Cover up. Get a wide-brimmed hat if your job allows it. Bucket hats, or fishermen’s hats, are designed to ward off sun and do a good job at it. Clothing is good, too. UV-protective clothing, or “sunware,” is designed to protect you from the sun. If you want protective clothing but would rather not wear a skin-tight rash guard, go to a hiking/camping/backpacking store. They’ll have UV-protective clothes that look like normal shirts, shorts, and pants. For regular clothing, color matters, with blue and red having the best UV-blocking capacity.

Make sure your diet is replete with nutrients that bolster your sun resistance. I’ve outlined eight of the main ones in this post. The biggest change I’ve seen has come from limiting omega-6 fatty acid intake (particularly from seed or vegetable oils; nuts and eggs and other whole food sources of PUFAs are more desirable and less problematic than the oils), eating more saturated fat to make up for it, and getting sufficient omega-3 from fish, shellfish, or fish oil supplements.

That’s it for today, folks. Thanks for reading and be sure to leave a comment!

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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