Dear Mark: Fish Oil and Exercise, Skipping Breakfast Study

Close up of a man take a fish oil capsule.For today’s edition of Dear Mark, I’m answering two questions about two recent studies. First, given that the omega-3 alpha linolenic acid (ALA) has been shown to reduce some of the positive effects of exercise on rats’ metabolic health, could the omega-3s found in fish oil (DHA and EPA) also nullify exercise benefits? Second, what are my thoughts on the recent study showing a link between breakfast skipping and subclinical atherosclerosis?

Ethan asked:

So what does the ALA study say about fish oil supplementation? Or do we expect this adverse effects were specifically caused by ALA and wouldn’t be caused by DHA or EPA?

Not sure, to be honest. There is one study from 1998 where dietary fish oil had beneficial immune effects in sedentary rats, enhancing the anti-tumor activity of killer T cells, but not in people who exercised.

What’s interesting about this study is that ALA and exercise were independently protective, but there was no additive effect. That is, if you just took ALA or just exercised, your body would get better at handling glucose and your body fat would be more insulin sensitive. But if you added it to exercise, the ALA would cancel out instead of enhance the effect.

There are some possible explanations. Maybe the rodents weren’t training hard enough. The authors note that this particular breed tends to go easy on the rat wheel. They don’t sprint, in other words. ALA (or fish oil) might pair better with more intense training.

These were rats eating extremely large amounts of flax oil (10% of calories) to get the ALA. That’s not a good idea for anyone, rat or human. Just as it’s not a good idea to eat 10% of your calories as fish oil. Smaller, more realistic omega-3 intakes at 1-2% of your calories could very well have a much different effect on exercise adaptations.

I wouldn’t worry too much. Even if fish oil impairs to some extent the metabolic adaptations of white adipose tissue, most of the research we have suggests that DHA and EPA supplementation enhances many other responses to exercise:

Of course, there’s the fact that fish oil seems to reduce post-exercise muscle damage and soreness. Is this good or bad? Taking fish oil to reduce muscle damage can speed up recovery and allow athletes to return to training or competition more quickly. But muscle damage is exactly what we recover from and, presumably, adapt to. Is fish oil speeding up the adaptation or short changing the stimulus?

In rats with atrophied muscles because of forced bed rest, eating fish oil inhibits the early stage of muscle recovery from atrophy—but they’re not training. They’re just ending bed rest. It’s not comparing apples to apples.

Fish oil actually increases muscle protein synthesis, as seen in the above study in elderly adults. It makes muscles more receptive to protein. While enormous doses of fish oil (10% of calories) may induce a huge anti-inflammatory effect that inhibits muscular adaptations similar to ibuprofen, most people aren’t (and shouldn’t be) eating that much fish oil.

I wouldn’t worry about taking normal doses of fish oil or eating fatty fish.

Hi there. Does anybody (ahem, Mark) have an inclination to weigh in upon the conclusions of this recent study concerning the linear relationship of arterial plaque preponderance and those who the least amount of daily calories for breakfast? I couldn’t find the ultimate sponsor of the study but even though it is another questionaire study, it is intriguing….

Sure, I’ll take a stab.

It’s not the first study to show that people who skip or eat small amounts of breakfast are more likely to have health issues. Plenty of other observational studies have found similar results.

  • Among Japanese adults, skipping breakfast was linked to greater body weight and waist size.
  • Among American young adults, breakfast skippers weigh more, have more abdominal obesity, and an elevated cardiometabolic risk profile.
  • On the other hand, among white and black American teenage girls, eating breakfast is linked to a lower body weight.

There are some confounding variables I find likely to play a role in this and other similar studies.

Healthy user bias. Everyone “knows” that skipping breakfast is bad for you, so breakfast skippers are more likely to exhibit other kinds of unhealthy behaviors like smoking, drinking to excess, not exercising. Sure enough, breakfast skippers eat more and exercise less, and they’re more likely to drink more alcohol and smoke more cigarettes. What if a breakfast skipper eats less overall, exercises regularly, drinks moderately or not at all, and never touches cigarettes? Is he or she in the same position as a breakfast skipper who does the opposite?

Is there a difference between the dietary composition of breakfast skippers and breakfast eaters? Probably so. In one study, Iranian children who skipped breakfast also ate way more fast food, sugary soda, salty snacks, and juice, and way less fruits, vegetables, and milk than those who ate breakfast. In the study mentioned earlier, the teen girls who skipped breakfast also ate less fiber (a marker of whole food/vegetable intake) and calcium. Is it breakfast skipping or is it all the junk and lack of nutrients?

They’re dieting. A common strategy when dieting is to skip breakfast. If you’re dieting, you probably have weight to lose, and it’s not surprising that people who have weight to lose have many of the diseases and disorders associated with extra weight. Maybe breakfast eaters are eating breakfast because they’re already healthy and at their goal weight.

Not everyone skips breakfast for the right reasons. How many balls of stress do you know who skip breakfast because they simply don’t have the time and then proceed to pig out in the break room, at lunch, and on through the rest of the day? Skipping breakfast is a very different experience when you’re a fat-burning beast.

In this latest study, we find our suspicions validated….

Breakfast skippers were more overweight. They were more likely to be smokers. They drank the most. They drank the most sugar sweetened beverages. They had more diabetes. They had higher fasting glucose, larger waists, and higher blood pressure. They were more likely to carry established cardiovascular risk factors.

While the researchers said that controlling for these variables did not abolish the link between small breakfasts or breakfast skipping and subclinical atherosclerosis, it greatly reduced the relationship.

I wouldn’t worry too much. If you currently employ a compressed eating window or IF by skipping breakfast and are the worrying sort, you could try skipping dinners instead.

Hope it helps.

Thanks for reading, everyone. Take care, be well, and chime in below with your own input!


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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38 thoughts on “Dear Mark: Fish Oil and Exercise, Skipping Breakfast Study”

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  1. Studies of animal fat consumption by granivores (rodents) cannot provide confident conclusions for facultatively omnivorous carnivores (humans).

    As for skipping breakfast, I’m in my eighth year of that particular n=1 experiment and it suits me so well I skip lunch too. Not hungry. Carnivorous diet too filling even with added carbs.

    Studies of fasting on malnourished captive humans (first-world random sample) cannot provide confident conclusions for well-nourished wild-type humans (the robust and dare we say handsome readers of this web site.)

    1. How did I know you would be all over these comments? Skipping breakfast is the best thing you’ve convinced me to do. So much more energy, more time to do other tasks and I can feel the fat sizzling.

        1. Timothy, I just spent some very enjoyable time looking at your website (by clicking on your name). Your writing is wonderful! Funny, informative. You should publish a book! The shovelglove thing is great! Makes me wonder if you ever wanted to try kettle bells. You certainly found your solution. . (Maybe you say it somewhere on your site and I haven’t found it yet). Nice job!

          1. Thanks so much, Andrea! Very glad you found the site useful. Still sledging and finding it more useful than kettlebells due to leverage. Still surprised sledgehammers have not caught on although maces seem to be growing in popularity (even though they are more expensive and less versatile).

            If you enjoy the writing, you might also enjoy the “Journal of Anthropological Engineering” on Instagram @urbanprimalist and the new blog at

            Nothing for sale, just applied anthropological research that needs peer review from people like you 🙂

  2. Does anyone else have trouble taking these rat studies seriously? I read that stuff and always feel like Somebody Up There must be laughing.

    Regarding skipping breakfast… Common sense is in order. I usually skip eating (IF) until around 11 a.m. or noon, at which time I may eat either meat and eggs or something more appropriate to lunch, such as a salad. This is normal for me since I don’t usually get hungry any earlier. I see no reason to go against my body’s preferred pattern just because some researcher has erroneously concluded that I’ll reach for cigarettes and junk food if I don’t eat normal breakfast food at a normal breakfast hour.

  3. Yes, there are a number of us who skip breakfast & are of a health weight, not overweight / don’t necessarily gorge on unhealthy Foods when we do eat. Somewhere there is info on how people with lower calorie intake, lowest calorie intake on average are the healthiest people/ live longer/ tend to be super agers.

    1. Maybe a useful link from Jason Fung on the breakfast topic –

      I fast through breakfast mostly because it’s easy – I’m drinking coffee and I’m just not particularly hungry in the morning. For those not hitting the above link, Dr. Fung notes that insulin response is typically muted in the morning, so it is actually the most efficient meal to eat. I’m with Dr. Fung in that the practical demands take over in that I really like to eat with my family at night. So, even though that would be a more rational way to do IF, it’s not appealing to me. With all of that in mind, I do wonder what the results would look like if those who did IF in the morning for long periods were tested. It would not surprise me if hormone levels adapted to individuals over time.

  4. Good bad or otherwise I’ve fallen into the habit of bookending two primal meals at noon and at 8 PM (with a protein shake in between). I do take two high potency DHA fish oil capsules per day with the HOPE that it helps with brain functioning, inflammation and heart health. Since “I am the Placebo” I believe it does. 🙂

  5. As far as the breakfast thing, it all goes back to listening to your body. Most studies don’t pertain to those of us who are fat burners (I personally don’t like the phrase “fat adapted”…sounds like I’ve adapted to being fat lol!) and eating nutrient dense food. If you feel great skipping breakfast then go ahead and skip it. Who cares what the studies say?! I am up very early and very active in the am and usually find myself hungry. Every now and then I’ll have a day like Saturday when it’s suddenly noon and I realize I never ate and feel fine. But if anything I’m more likely to skip dinner…that just seems to suit me better.

    1. Interesting. I’m the exact opposite. A late riser by nature (11am on a Saturday). I have to be up for an hour or two before I can even stomach the thought of eating food. It’s usually several hours before I actually feel like eating. But every now and then I find myself up early on Saturday, cooking bacon & eggs.

  6. Okay, I’ll go with an N=1… son, who is a 17 year old very healthy, active teenage boy, with a lean but well-muscled physique, rarely eats breakfast. Why? He just doesn’t feel the need to. My guess is that he has “perfect” metabolism because his parents (me and hubby) have raised him since infancy on a natural life course (no vaccines, complementary/alternative health practices, lots of time in nature, activities that involve being outside while working the body, and whole foods). He doesn’t experience shifts in energy and can obviously go great lengths on IF when he chooses to do so. I sometimes wonder how all of the children of Primal/Paleo parents will turn out. Could it be possible we will be offering up to the world a generation of metabolically “near-perfect” humans? One can hope. It is, at least, better than the alternative.

    1. Beautiful work with your son, I try to do the same with mine. As for metabolic near-perfection, how would we know it? We might compare ourselves to those Native Americans who, until recently, grew well over six feet tall and hunted bison on foot.

      What is sure, however, is that the gulf between the healthy “haves” and the sickly “have-nots” is growing dramatically — perhaps even to unprecedented levels of inequality. How will our children fare in a world with so many peers who are metabolically crippled? Will they thrive and be free, or will they be punished by the majority for their “privilege”?

    2. If this is not the comment of the week I will be surprised 🙂

      “Could it be possible we will be offering up to the world a generation of metabolically “near-perfect” humans?”

    3. 17 – 25 year old’s can gets away with anything – just look at the amount of partying on campus students do, their bad diet, and the ability to still somehow have a six pack – as Mark mentioned once “at 20 years old they were consuming kegs and had a six pack stomach, by 30 they were consuming 6 packs and had a keg stomach”.

  7. Here is a possible explanation, Flax contains cyanide and maybe the cyanide inhibited the effects of the ALA. Anutra chia, the safest source of ALA has no cyanide and may tell a far different story with those lazy rats.

    ALA is the only essential Omega 3 and it converts to DHA and EPA tailor made as our bodies require it. Anutra chia does many other things especially in cell replication. ALA gives us the healthiest cells possible. It also creates an enzyme called Telomerase which conditions and repairs our Telomeres after cell division. ALA does a lot more too.

  8. The latest breakfast study, proudly brought to you by Kellog’s corn flakes.

  9. As a not breakfast eater. I tend to eat more at night so I am just not as hungry in the morning. My weight and BMl are fine, thanks. I think for more non- breakfast folks may eat too much at night. Of course overeating can occur any time of day..or night! Thus the extra weight. Pace from n.c. Do not need a study for that idea.

  10. One possible issue with breakfast skipping is the disruption to circadian rhythm. I had some severe hormonal disruptions trying to intermittent fast by skipping breakfast which among other things, manifested into the worst insomnia you could imagine. Even a brief peruse of the work of Bill Lagakos or Jack Kruse will back this up with studies.. Get some morning light and eat a big breakfast!

    1. Listen to your body, man! I’m the exact opposite. Eating breakfast makes my stomach queezy, and my mind/body tired and groggy all day.

      1. There is indeed no substitute for honest, n=1 research. Discovering what works for ourselves is one thing; generalizing those results to the entire human race is another.

  11. Interesting read. I’m not a breakfast person. Never have been. I don’t even remember eating breakfast before school as a child, though it was certainly available. It makes me feel queezy in the stomach. I have to be up for at least an hour or two before I can even force myself to eat breakfast (social etiquette sometimes requires it), but generally I’m up for several hours before I start to feel like eating (I can generally go a lot longer). I have gone through periods where I’ve tried to force myself to eat breakfast (most important meal of the day, right?), but it always leaves me feeling like shit for the rest of the day. Now I just run with it, knowing that it’s perfectly natural, and healthy.

  12. Hi there, This is my first foray into commenting, although I am an extremely interested onlooker to this wonderful site.
    I would very much like to hear views on skipping evening meals. I quite like that idea and sporadically eat a primal breakfast, salad and protein for lunch then fast from about 1pm till 8ish next morning. Alas I suspect it is a bit “anti social” but it seems to suit.

    1. Interesting Annette. If I’m reading this correctly you eat all of your meals between 8 AM and 1 PM, that’s a very narrow 5 hour “feeding window”, so you are doing IF for 19 hours daily? On top of that you use the term “sporadically”, does that mean you often skip breakfast and just eat one meal a day? Seems a little extreme but if it works for you more power to you, but if you start getting fatigued maybe decrease that IF time period some and make sure to always get two meals.

    2. Annette, when we eat our ancestral, nutrient-dense food, many report eating habits falling into line as a side effect. Many of us didn’t decide to skip meals, it just started happening because we weren’t hungry.

      Who could look into your blood chemistry and tell you “no, skip breakfast instead”? You are a unique person, with unique genetics, adapted to a unique environment. Your hormones are telling you skipping meals suits you at the moment. They’d be singing a different tune if you weren’t well nourished.

      Is it anti-social to fast while the others eat? Well, is it anti-social for others to eat while we fast?

    3. My eating window is 6 am to noon-ish, I’m up at 4 am to do my 2 mile walk, eat breakfast, have my version of Bulletproof coffee for a mid-morning snack, eat lunch, and call it good. Leaves my evenings free to do other things, fall into bed at 9 and out.
      I will shift my eating window, or just eat 3 meals in a day if I have an invite for an evening meal, then fast the entire following day.

  13. Correlation does not equal causation. The best I example I ever heard was a fake study that “proved” that eating ice cream causes shark attacks. The study showed an almost perfect relationship between ice cream consumed and number of shark attacks.

    Listen to your body and eat when you are hungry. Best way I know to figure what true hunger feels like is occasional 24 hour fasting.

    1. Obviously shark attacks cause people to eat ice cream as a method of self comforting. Probably shark attacks cause an increase in the consumption of beer.

  14. Mark – I expect those dam rats were not sticking to the primal blueprint exercise regime !

  15. HI,
    For every health problem, there are foods with supplements that could suppress the effects, prevent it or even cure in some cases. like I usually say, food, vegetables and water are the best medications. There are several studies on the effects of flax seeds extracts on acute asthma. there’s other food supplements that can help you reduce the risks of asthma attack

  16. hi
    My university teacher tell me that fish oil helps with brain function and memory, I take two a day and find i’m less stressed before exams… and note that my hair growing smoother

  17. Speaking of skipping meals, does anyone find that they ave stomach pain after breaking a fast longer than 16 hours or so?

  18. there is many benefits of fish oil. It is best for skin. I use daily in night. I am so happy with this results….

  19. Good bad or otherwise I’ve fallen into the habit of bookending two primal meals at noon and at 8 PM (with a protein shake in between).