Hello, I’m hearing a lot that eating at maintenance is good for keeping the immune system strong during the pandemic. If I were to do a small calorie deficit like -250 would this be a significant trade-off in favor of wanting to lean out a bit for immune health? According to US Navy body fat calculator I’m around 15 % (probably not an accurate method but one I’ve been consistently using), and was hoping to reach around 12% body fat for the summer. Immune system is important to me during the pandemic, but like a lot of guys I like having periods where I lean out a bit. I’m currently maintaining around 175 lbs.
This would have no impact on your immune system: https://podcasts.apple.com/us/podcas…=1000470680259
Thank you for the link and quick response. I will give it a listen.
Are there guidelines on how big a caloric deficit needs to be before it would start impacting the immune system? Anecdotally, I’ve noticed a huge increase in illness the few times that I’ve tried to do a caloric deficit of 750-1000 calories a day, but there could be confounding factors there.
There aren’t any impacts of a calorie deficit unless you’re malnourished.
Do you have any recommendations of where I can learn more about the research and specific evidence regarding large caloric deficits and the immune system? Is this something that has been thoroughly debunked, or is there just a lack of evidence for a link?
I’ve noticed such a profound correlation between a large caloric deficit and increased frequency of illness that I wonder if I’m doing something specific that could be causing me problems. Based on a quick estimate, I’ve gotten sick about 5-10x as often during periods of significant caloric restriction compared to the rest of my adult life. The one time in the last decade that I got very seriously ill with the flu was during a period that I was experimenting with the paleo diet and probably eating less than 1500 calories a day.
I certainly wasn’t underweight at these times; is it possible that I had a significant vitamin deficiency after changing my diet for only a few weeks? I’m sure I had reduced food variety at those times, but it doesn’t seem like that dramatic a change. Alternatively, is it possible that psychological stress and/or poorer sleep caused by dieting could be contributing to increased frequency of illness?
Did you listen to our podcast?
I did listen to it about two months ago, and I just skimmed through it again. I didn’t notice any diet/nutrition content; it seemed like about 10 minutes of general immunology overview and 20 minutes of debunking the idea that exercise suppresses the immune system. Did I miss something, or are you referring to a different episode than the one you linked above?
I believe we specifically talk about obesity and the immune system. Reducing your calories does not reduce your immune’s system function. However, carrying too much body fat does.
I just listened to the podcast again, and there is no mention of obesity that I noticed, although Austin does briefly mention body composition changes as a result of decreased step count. The only discussion of diet is a brief digression about factors that can alter salivary IgA levels. Maybe I’m completely missing something, but the podcast seemed to be entirely focused on exercise.
Regardless, I’d love it if you can point me to some resources where I can learn more about the evidence on this topic. I have personally experienced a strong correlation between significant caloric restriction and illness, and I’ve heard other generally trustworthy and well-informed people (most recently Greg Nuckols) suggest that they think there is some relationship between caloric restriction and illness.
I spent a few minutes looking for evidence on this topic, and I didn’t find anything particularly informative outside of a few rodent studies. However, I did find research suggesting that chronic stress can have a negative impact on the immune system. To the extent that significant caloric restriction represents a chronic stressor (and it certainly does for me), could that have an impact on the immune system? There also seems to be a link between sleep and immune function, and I definitely find that my sleep is much worse when I’m in a large caloric deficit.
If there is a body of evidence supporting the idea that significant caloric restriction is not at all correlated with illness, I’d love to read it and update my position.
It may have been the COVID podcast, as they do tend to run together in my brain.
I do not think there is any evidence for calorie restriction and immune “compromise”, rather the opposite if someone is carrying too much fat mass.
Calorie restriction isn’t really a chronic stressor unless we’re talking about malnourishment. Again, carrying too much adipose tissue would be a deleterious stress.
Overall, if someone is carrying too much adipose tissue, calorie restriction may be beneficial for immune system, sleep, etc:
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Thank you; I will read through those and digest them as best I can.
One point I’m curious about:
Calorie restriction isn’t really a chronic stressor unless we’re talking about malnourishment. Again, carrying too much adipose tissue would be a deleterious stress.
I understand that obesity is a stressor, but you don’t find that hard dieting increases your stress level? If I’m on significantly restricted calories, I find myself constantly thinking about food, either worrying about not having the right food available, dreading eating more unpalatable food, or just trying to suppress hunger. Pretty much any social engagement becomes a source of stress, and work is more stressful as I worry about the impact of hunger and distraction on my performance. Am I very unusual in this experience, or does this kind of stress just not constitute a “chronic stressor” in the sense that the literature is using the term?
No, I don’t find that small to moderate calorie deficits represent a significant stress for myself and the majority of those willing to engage in that behavioral change. Larger deficits may increase the “dietary RPE” sure, but even then- not reliably.
I think if someone is very hungry and has substantial barriers (along with limited resources) to overcome with respect to adherence, this can be problematic.
Interesting; I guess I’m just an outlier in that respect.
I had a chance to read through some of those studies, and there’s a lot of interesting stuff in the there. I was a bit confused by the caloric restriction protocols in most of the studies. They claim to be reducing calories by 25-30%, which seems like a fair amount, but the actual weight loss numbers don’t support that. In the inflammation study and the mood/sleep/sexual function study, the participants only about 15-16lbs over two years of caloric restriction, suggesting that the actual daily caloric deficit was less than 100 calories. The T-Cell study doesn’t give enough information to really do a good job of running the numbers, but a 10% weight reduction over six months in people with a BMI of 28, assuming roughly average heights, gives us a daily deficit of about 300-350 calories. Do you think we can safely assume that the impact of these deficits is similar to the impacts of deficits 3-10x larger?
Also, it seems like all of the immune studies were really measuring the medium/long term effects of weight loss, not the shorter term effects of caloric restriction. It’s plausible to me that the positive effects of losing 15-20lbs could overshadow any potential negative effects of a small caloric deficit. I’d be interested to see a study where we took subjects, put them on a large caloric deficit for a week or two, and then either tested immune markers or observed sickness rates. Unfortunately, I’m not able to find a study like that.
On the other hand, the paper on sleep study reported some findings that certainly make me question my assumptions. I was very surprised to see that two days of almost complete fasting did not impact sleep or cognitive ability, since that definitely runs counter to my experience. In the other direction, I was surprised to see that a 2700 calorie high fat meal, eaten less than two hours before bed, had no effect on sleep. If I ate the equivalent of an extra large pizza, I doubt I’d be able to sleep at all two hours later. Assuming those findings are legitimate, it’s clear to me that my experiences must be far outside the norm.
Regardless, thanks for the links; definitely learned a lot!
I had a chance to read through some of those studies, and there’s a lot of interesting stuff in the there. I was a bit confused by the caloric restriction protocols in most of the studies. They claim to be reducing calories by 25-30%, which seems like a fair amount, but the actual weight loss numbers don’t support that. In the inflammation study and the mood/sleep/sexual function study, the participants only about 15-16lbs over two years of caloric restriction, suggesting that the actual daily caloric deficit was less than 100 calories. The T-Cell study doesn’t give enough information to really do a good job of running the numbers, but a 10% weight reduction over six months in people with a BMI of 28, assuming roughly average heights, gives us a daily deficit of about 300-350 calories. Do you think we can safely assume that the impact of these deficits is similar to the impacts of deficits 3-10x larger?
10% weight reduction is ~ 2x the limit for clinically significant weight loss. Also, as you know- weight loss is not linear and weight maintenance is complicated. I don’t necessarily share your concerns however, as if there was a robust effect of a calorie deficit on the immune system, we’d be able to see it.
As I mentioned earlier, all bets are off if you’re malnourished.
Also, it seems like all of the immune studies were really measuring the medium/long term effects of weight loss, not the shorter term effects of caloric restriction. It’s plausible to me that the positive effects of losing 15-20lbs could overshadow any potential negative effects of a small caloric deficit. I’d be interested to see a study where we took subjects, put them on a large caloric deficit for a week or two, and then either tested immune markers or observed sickness rates. Unfortunately, I’m not able to find a study like that.
Fortunately, any short term effects here on infection/sleep etc. would also be minimal, given their complex nature. Thus, I’m less interested in this- though some of the religious fasting studies are short term and show minimal effects: Ramadan Fasting Exerts Immunomodulatory Effects: Insights from a Systematic Review - PMC
Fair enough; thanks for your insight.