Calorie Restriction: My Theory and Practice
Like most futurist-oriented people, I am fascinated by the idea of long-term life extension—the notion that eventually people will have life expectancies of hundreds of years; thousands of years; or even more. Although medicine has a ways to go in this area, one obvious approach is to take low tech steps to increase one’s lifespan in hopes of living long enough to take advantage of possible future advances. i.e., to roll with +1 dice. Besides the obvious steps like wearing seat belts; getting regular exercise; eating a lot of fruits and vegetables, calorie restriction presents itself as an intriguing possible method of life extension.
In this essay, I will attempt to briefly define calorie restriction; assess how useful it might be; speculate about how it might be useful; and use the foregoing to justify my own personal approach to calorie restriction, which I will describe presently. Of course I welcome comments and criticisms, especially since I am messing around with my own health.
I should note at the outset that I have no formal training or credentials in medicine nutrition or anything like that. I’m just an attorney.
I should also add that my approach to calorie restriction is not a diet in the sense of being a weight loss strategy for people who cannot control their eating. This is not a weight loss post! I do not describe in this essay how I control my eating; control is assumed.
Last, my general approach is one of no regret. i.e. My main priority in calorie-restricting myself is to avoid doing anything too radical in terms of loss of quality of life or risk to my health.
I. What is Calorie Restriction?
Wikipedia defines “calorie restriction” as follows:
Caloric restriction (CR), or calorie restriction, is a dietary regiment that is based on low calorie intake. “Low” can be defined relative to the subject’s previous intake before intentionally restricting calories, or relative to an average person of similar body type.
So immediately we see a problem—the concept of calorie restriction is ambiguous. How am I supposed to evaluate and possibly implement calorie restriction in my life if I am not even clear on what it means? This is not just a problem for laymen like me. Imagine you are a researcher who is studying the effects of calorie restrictions in lab chimps. How do you feed your control group of lab chimps? Do you let them eat donuts and potato chips ad libitum? Do you limit them to chimp chow? Without a clear definition, this is a bit of a conundrum.
In fact, one individual has argued that the difference in treatment of control animals may be part of the reason why two studies on calorie restriction in monkeys had different results:
Further, the NIA study control monkeys were not truly fed ad libitum, unlike the WNPRC study. The regulated portioning of food for the NIA control monkeys may be a slight restriction and, thus, largely prevented obesity. Studies of 10% CR have been reported to increase lifespan in rats compared to ad libitum controls – even more than 25% and 40% CR20. The NIA control monkeys may experience survival benefits from this slight restriction.
http://www.crsociety.org/science/nia_monkey_study
Another individual states as follows:
“Both the NIA and U Wisc studies need to be considered together for proper interpretation. It is clear that the U Wisc “controls” differ from the U Wisc CR group and BOTH NIA groups, and are probably most like the general populations of developed countries.
Because we at NIA wanted to avoid the criticism leveled at many rodent CR studies that controls are overweight and sedentary, we specifically designed our dietary conditions to supply an adequate, but not OVERadequate, caloric intake.
The bottom line is that, for most people (who are more like the U Wisc controls), CR may indeed provide both health (BOTH studies agree on THIS) and longevity benefits.....and of course, most important.....more “healthy years.”
For purposes of this essay, I will offer the following definitions:
1. “Mild calorie restriction” = restricting calories sufficiently so that you avoid gaining large amounts of weight.
2. “Moderate calorie restriction” = restricting calories sufficiently so that most of the time you are towards the bottom of your metabolic range.
3. “Severe calorie restriction” = restricting calories sufficiently so that you end up spending your time significantly below typically fit people in terms of muscle mass and/or body fat.
The first and third definitions are pretty straightforward, although it’s worth noting that a lot of people engage in mild calorie restriction unintentionally, just through the operation of their natural system which regulates their appetite/urge to eat/urge to stop eating (John Walker calls this the “food clock.”)
The second definition requires a little explanation. From simple observation, it appears that small changes in one’s energy intake result in corresponding changes in one’s metabolic rate. So that if your weight is stable but you eat a little more or less than usual, you might notice that you are a little warmer or cooler than usual. Evidently the body can and does make small adjustments to its metabolic rate in response to changes in food intake. This is also consistent with dieters’ reports that they feel cold when dieting.
II. Does Calorie Restriction Work in Humans?
It seems quite likely that mild calorie restriction works in humans based on the observation that fat people have significantly greater mortality than thin people.
For example, as illustrated by the charts here:
http://www.nejm.org/action/showImage?doi=10.1056%2FNEJMoa1000367&iid=f01&
Of course one cannot know this for sure since there is no ethical way to do a large controlled experiment, but still it’s reasonable to infer cause and effect: Common sense says that being fat puts a lot of abnormal extra strain on your system almost all the time. In any event, there seems to be little downside to mild calorie restriction.
A more interesting question is whether moderate calorie restriction works in humans. Common sense says that it ought to be beneficial based on the idea that slowing one’s metabolism ought to slow the aging process, all things being equal. One interesting area of research is studies which look at the effect of modest weight loss among obese people. Is someone who goes from 250 pounds to 225 pounds and stays there more healthy than someone who goes from 210 pounds to 220 pounds and continues to gain weight? If so, part of the difference might be that the second person is towards the top of his metabolic range while the first person is towards the middle or bottom.
The Calorie Restriction Society web site links to a couple presentations which argue that cancer is actually a metabolic disease related to having too much energy in play. I’m a bit skeptical of this claim, but it does seem to me that you are inviting trouble by having extra energy floating around in your system.
As for severe calorie restriction, the jury is still out. I don’t put too much stock in the left side of the J-shaped curves comparing body weight to mortality. Surely a lot of underweight people have serious latent health problems. What’s more interesting to me is that the curves flatten out between BMI of about 19 and 23.5. This suggests to me that one can realize most of the benefits of reduced body mass by being normal weight and that after that, if there are any benefits, it’s diminishing returns.
III. My Approach to Calorie Restriction
I have decided to adopt an intermediate approach to calorie restriction, i.e. the aim is to stay thin and be towards the bottom of my metabolic range most of the time. The health benefits to staying thin are pretty clear; there doesn’t seem to be much downside; and frankly there are a lot of social benefits. The benefits of staying towards the bottom of my metabolic range are more iffy, but again there doesn’t seem to be much downside to it. (Putting aside issues of health, the main downside is that it happens pretty frequently that I will have a meal and eat less food than I would have liked to eat.)
Severe calorie restriction seems too speculative to me to be worth the trouble. Particularly given the social costs and the likely diminishing returns problem. I like having a somewhat muscular appearance as opposed to a gaunt appearance. Since my main priority is to avoid regrets, I am not willing to go this route without pretty solid evidence of benefit.
IIIa. The Nuts and Bolts
What I do is this: I have a basic daily diet which I believe is reasonably healthy and well-balanced. Although it is somewhat flexible, it contains roughly the same proportions of macro-nutrients and is roughly the same amount of calories each day. From careful observation, I have determined that my basic daily diet is about 500 to 600 calories short of my actual daily caloric needs. i.e. if I stuck to my basic daily diet and ate nothing more, I would lose about a pound a week. I add a small supplement of extra food to my basic daily diet if I work out at the gym in order to balance out the exercise. (Interestingly, I once measured and it seems my basic daily diet, including the exercise supplement, is about 2800 calories. This seems pretty high for a man who is thin, slightly below average height, and only slightly muscular in build. I’m not sure what to make of it.)
I weigh myself every morning and calculate a 7-day moving average of my weight. I then subtract this number from a pre-determined reference weight and multiply the result by 100. This is the number of additional calories I consume that day in the form of reasonably healthy foods. The idea is to eat close to the minimum to maintain weight, thus staying thin and towards the bottom of my metabolic range.
Now and then my weight spikes upward when I have an event which involves a lot of eating; after that it drifts back down again. I’ve been calorie-restricted in this way for some time now. I feel perfectly fine but after every meal I feel like I could easily eat more. I pretty much never get heartburn anymore. I usually wake up quite hungry. These are about the only effects I have noticed.
IV. Self-Criticisms of My Approach
In the interest of rationality, it probably makes sense to offer some self-criticism:
1. I found the above scientific references only after I had settled on my approach to calorie restriction. So there is probably a certain backwardness about my reasoning. My conclusion is based more on my own intuition, reasoning, observations and common sense than on scientific research.
2. It never occurred to me to regularly measure my body temperature before and after starting this program. Which is unfortunate because it may have given me some useful information about the effects of my diet on my metabolism.
3. There’s really no way to measure if any of this is having an effect on my rate of aging. Without this sort of feedback, I’m pretty much shooting in the dark.
V. Conclusion
So that’s about the extent of my self-experiment. It’s a bit frightening that I’m putting my own health on the line in the face of so much uncertainty. At same time, it seems like a reasonable, conservative approach which is unlikely to lead to regrets. Of course there is an excellent chance I will never know how much of an impact my lifestyle had on my overall health.
Anyway, I welcome any intelligent thoughts, suggestions, constructive criticism, etc.
I practice intermittent fasting in which I restrict my consumption of carbohydrates and protein to a six hour window most days in part to promote autophagy.
The NIA rhesus monkey study found:
The NIA study ran for 20 years on two groups of monkeys, “early onset” monkeys who started CR (or being in the control) at a young age and “late onset” who were older. As you’d expect, there were more age-related deaths in the “late onset” group (80 out of 90 monkeys) than the “early onset” (19 out of 90).
By contrast the WNPRC study found that CR did have a positive effect on lifespan:
The WNPRC study had 76 monkeys, 19 of which died from age-related causes.
There’s a long discussion section at the end of the NIA article talking about differences between the two studies.
That line from the abstract is an outright lie. Check out the graphs. The actual survival rate was something like 50% vs 60%. CR won, but it was not statistically significant. What this really showed was a trade-off between “age-related mortality” and frailty, although the latter is usually considered “age-related” in humans.
I think CR is a bad idea compared to intermittent fasting after reviewing the available studies and expert opinion on those studies. Here’s one cautionary editorial: http://healthland.time.com/2012/08/29/want-to-live-longer-dont-try-caloric-restriction/
I don’t have all the evidence about it loaded into my head right now, but I can go dig it up later. What I recall is that while there was a life extension benefit for sedentary, high bodyfat lab animals, there was no benefit recorded for wild caught, normal bodyfat animals.
I also personally know people who did CR and regretted it because their hormone levels are now out of whack.
I also think that IF would be easier to maintain than a permanent reduced caloric intake. From what I have read IF does not decrease metabolism that much and energy levels are pretty much the same.
Yes for me but only after a transition period.
Yeah, which means you can exercise without wanting to die.
Thank you for your response. When you refer to “CR,” do you mean calorie restriction which is mild, moderate, severe, or something else?
Under my personal approach to calorie restriction, I eat an average of about 3000 calories per day. So it’s hard to imagine my hormones getting too out-of-whack.
I will check out the concept of intermittent fasting.
I’m unsure as to parameters the people I spoke with were using. Something in the realm of 1200-1500 calories a day for 5′11″ish people who are lean.
3k calories is bulking for me and I’m fairly active, so I’m confused.
Well that’s a big problem. As I alluded to in the main post, the phrase “calorie restriction” is ambiguous. So when you argue that “calorie restriction” is a bad idea, your point remains somewhat unclear.
In what way were their hormone levels affected? I can’t even begin to guess.
I don’t have their numbers offhand but one of them got regular blood panels and reported testosterone crashed and didn’t recover after they went back to a normal diet (and exercise), also several hormones relating to hunger were screwy and they confirmed they can easily eat 5k calories now and not want to stop. Other did not have blood panels but reported similar symptoms.
People might be a bit too quick to associate whatever health problems they have to whatever intervention they were running at the moment they got them.
Suddenly being able to eat far more than one could earlier right after getting off a diet that explicitly restricts calories seems like a fairly safe causal conclusion.
He has been off of it for over a year.
If slowing metabolism increases longevity, how come exercise, which increases metabolism, is beneficial?
As an endurance runner with a BMI of ~20 on an eat-as-much-as-you-like diet, is my calorie consumption is optimal for longevity?
I think that’s a really good question.
I can throw out a few ideas, but they are somewhat speculative:
Perhaps one can analogize the human body to a car. If you drive a car all the time it will wear out quicker. But if you leave it sitting in your driveway, it’s also bad.
If you increase your metabolism through exercise, at least you don’t have the problem of extra energy sitting around in your body which can be used through mischief.
A lot of exercise really does wear out your body quicker, but the benefits outweigh the harm.
The increased metabolism from exercise is primarily focused in your muscles which can handle it; muscles are not prone to cancer.
Edit: Oh, and of course Number 5: My hypothesis is dead wrong.
Since I think mild restriction is better than ad libitum eating, I would guess “no.” Although your low weight suggests that for you, ad libitum eating is somewhat restrictive anyway.
I’ve been eating less calories since 1998, and I found starting at what was 3200 kclas, I had to reduce down to 1800 kcal to lose weight.
I did it stepwise starting at 2800 kcals for 3 months, incurred no problems but lost no weight.
I dropped from 3200 to 2800, then to 2500, 2200, finally to 1800 in the span of 2 years(or so).
I had previously developed a Lotus spreadsheet based on the SR 12 database and checked my diet daily.
In one period I was trying to lower weight to see if it would reduce my BP, and I dropped to 172 # from 206.
I did gym exercise 3 or 4 times per week.
My results were, not much drop in BP, and no real loss in medication. The only real cahnges were my wife and I basically controlled our diets.
At 83 yo, I can say I believe that process helped us realize that diet control is necessary, certain foods should be avoided, and certainly caloric intake must be controlled, but it must be learned and able(easy) to do.
Yes, we will still eat a what-a-burger and fries, but not often, and in other restaurants we select carefully to avoid mostly greasy sauces. Fats by themselves are very high in calories, and can be absorbed without control into the lymph system, where they avoid the control of the liver and kidneys.
For exercise, we finally quit the gym because we were wearing our joints out.
WE don’t run now, we walk and we have a stationary recumbent bike in our living room. Mostly for working the leg muscles without strain.
Caloric intake is much more important because exercise doesn’t burn many calories.
I don’t know how to measure CR in terms of %, I doubt it could be 3200 − 1800 = 1400⁄3200
Some 44%? altogether.
My wife and I are older than our parents, in good health, and have 6 ggchildren.
Regards
My VLCD experiment that started about 7 weeks ago gradually lead to a diet pretty similar to yours, about 500 kcal short every day estimated from my recent weight loss. This probably amounts to about 1000 kcal less than I used to eat to keep my weight. I also compensate for the exercise now. Anything lower than that seems to make me lethargic unless I take ridiculous amounts of stimulants. Replacing some of my meals with powder products helps to keep the intake low, since there are fewer real meals where I have to watch what I eat.
Regarding your speculations about metabolic rate, I get cold much easier now. I wake up freezing if I don’t put enough clothing on at night. This has never happened before. Of course, fat keeps you warm too.
Yes, I imagine that you could transition from a diet into moderate calorie restriction. I didn’t really discuss my thoughts about dieting since it wasn’t a diet post and also weight loss is necessarily a temporary process.
You could also read my comment as “severe calorie restriction didn’t work for me that long, not even for weight loss”. If I couldn’t keep it up longer than a couple of weeks even when I had excess fat, it’s unlikely I would be able to keep it up when thin.
Well I wouldn’t call what you did “severe calorie restriction,” since it doesn’t really fit into any of my definitions. Eating less than your caloric needs is necessarily a temporary situation.
Well my post assumes that one has control over one’s eating. If you cannot control your eating, then calorie restriction for longevity is kind of a moot point for you.
I actually have some ideas about how one can control one’s eating but I am disinclined to share them here until I am more satisfied that they work. Too many people go online to kvell about their diet strategy only a few months in to their diet. That’s arguably the equivalent to releasing software which hasn’t even been alpha tested.
That’s not what I said.
Perhaps you’re right. I’ll not bother you further.
You seem to have implied it:
I took that to mean that you engaged in calorie restriction sufficient to result in weight loss but were psychologically unable to stick with it. i.e. you were unable to control your eating.
It’s up to you, but we need to be clear about what we are discussing. There’s a difference between calorie restriction—as I have defined it—and dieting.
That’s not how I read that chart and the many similar ones showing mortality as a function of body mass index.
If, for the sake of argument, we make the (unreasonable and wrong!) assumption that the variance in mortality is caused by the variance in body mass index, it looks to me more like being fat is much less dangerous than being thin. Look at the shape of the curves as you move away from the minimum mortality trough around BMI 19-26 or so (which is slightly higher than many official guidelines for ‘normal’ weight). Sure, mortality increases steadily as BMI increases from the minimum, but it shoots up much more steeply as BMI decreases. Indeed, for all subjects, the BMI=17.5 bucket (the only one thinner than the minimum mortality trough) has higher mortality than the BMI=42.5 bucket (significantly fatter). To put that in concrete terms, the mortality risk for a six-foot high person (1.83m) is higher if they weigh 130 lb (59 kg, 9 stone 3 lb, BMI 17.5) than if they weigh 310 lb (142 kg, 22 stone 6 lb, BMI 42.5).
There aren’t any data points in the buckets below BMI 17.5, and my guess is that’s because people tend not to have BMIs in that range—or if they do it’s not for very long, because they die. Of course, that’s often because—contra the assumption above- causality there often clearly runs the other way: people who get terminally ill often lose an awful lot of weight before they die (cachexia).
Curves like the one you link to are a common finding. Another common finding is that the curve shifts to the right as people age—i.e. the lowest-risk BMI increases over time for an individual, and being officially ‘overweight’ (BMI 25-30) has lower all-cause mortality than being officially ‘healthy weight’ (BMI 18-25). (Can’t instantly put my hand on a good example, but this study found the mortality minimum was 27.1 for people aged 70-75.)
That seems to be to be at least some evidence against the idea that to maximise your lifespan you should make your weight decrease as your life progresses.
This is very difficult stuff to get robust data about—it’s awash in complex correlation/causation stuff, and getting hold of data is very hard. It’s also overlaid with a lot of moralising that seems pretty unhelpful.
I would agree with you if we were looking only at that chart and making no use at all of any other knowledge or common sense. But if one adds in other knowledge and common sense, it’s reasonable to believe that there is cause and effect on the right side of the chart.
The left side is more difficult to interpret since there are many unhealthy conditions which can cause weight loss.
This is true of just about any data concerning human health. But health decisions need to be made. Under the circumstances, I’m reasonably comfortable with (1) not smoking; (2) restricting calories enough so that I do not become fat; (3) eating plenty of fruits and vegetables; (4) exercising regularly. I think there’s a good chance that these things will improve my longevity and perhaps more importantly I think it’s pretty unlikely that I will be significantly worse off for having done these things.
My concern is particularly describing “thin” as healthy, or low risk for mortality. If by “thin” you mean BMI 18-25, then I’m with you, but that’s officially labelled “healthy” or “normal” weight and is not what most people mean by thin. The official “underweight” category (<18) is much riskier than the official “overweight” category (25-30). The risk profile either side of official “healthy” weight is not symmetrical—and indeed there are sound reasons to think that tending towards the top end of “healthy” and in to “overweight” as you age is the least-risk track for weight over a life course.
Indeed—eating disorders being a particularly notable group. I am concerned that erroneous messages that “thin is good and healthy” are exacerbating those problems, causing significant avoidable mortality. Thin is not good and healthy.
(You suggested “being fat puts a lot of abnormal extra strain on your system almost all the time”; I suspect being thin does too, since it means your body will your body will struggle to find sufficient metabolic resources for things like healing processes, regeneration, the immune system and cellular repair mechanisms.)
The curves on that graph for “healthy subjects who never smoked” should exclude people with unhealthy conditions and diseases that affect their weight, and show the same pattern, albeit reduced—you have to get up in to the “obese” category (plotted at BMI ~31) to get a mortality risk as high as the “underweight” one.
One might be able to make a case that there is a particular subset of underweight people who do not experience the significantly raised mortality risk that other underweight people do, but I’ve not (yet?) seen a convincing one.
Sure—but it’s not simple and one-way. One can also reasonably interpret the data to find “being low socio-economic status” as a causal factor of both higher BMI and higher mortality risk. (And of course there are also diseases that cause weight gain and increased mortality.)
Absolutely—that list seems a good distillation of my understanding of what the evidence supports too.
I didn’t precisely define the word “thin,” but what I had in mind was “not fat.” I suppose that BMI 18-25 is roughly what I mean by “thin.” I consider myself to be “thin” even though my BMI of 24 puts me close to the official line for “overweight.”
Depending on your definition of “thin,” I would agree with you. And it’s part of the reason I am not engaging in what I have defined as “severe calorie restriction.”
I doubt that they do so completely. Between people lying about their health and simply being unaware of latent serious health problems, I am pretty confident that the curves for “healthy people who never smoked” include a decent number of people who are actually not healthy.
It would depend what data you are looking at. If you look at the entire universe of general knowledge and common sense, this seems unlikely—at least as the primary factor.
Aha! I think we’ve found the main source of our disagreement here, and it’s purely terminology. Totally agree that maintaining a BMI around 24 is a reasonable, broadly-supported aspiration (all other factors being equal), particularly if you’re younger than middle age.
Agreed it’s probably not the largest effect, but I do think there’s good reason to think there is an effect going that way. There seems to be a growing amount of evidence that low socio-economic status is bad for mortality, mostly indirectly (makes you more likely to do things like smoking, eating a diet with less fresh fruit and vegetables, etc) but also directly (low social status makes you die sooner), although of course separating that out of any naturalistic data is hard. (See e.g. this, and the older Whitehall studies.)
This is subject to the same cause and effect issues you alluded to earlier. It’s reasonable to hypothesize that worse-than-average impulse control is likely to result in both low socio-economic status and overweight/obesity.
Anyway, for my purposes it doesn’t really matter. The evidence is strong enough that at a minimum I’m willing to stake my health on the claim that it’s better for one’s health to avoid getting fat.
I’ve three issues with such reasoning :
It’s quite blunt and non-discriminating, while people have very different metabolism. I don’t practice any “calorie restriction” (I just try to avoid eating too much fat/sugar), I eat as much as I feel like eating, and yet I weight like 55kg, and I know many other people eating “as much as they want” and not having any overweight problem, quite the opposite.
It just focus on “calories” without any consideration of what kind of calorie (ie, what kind of food), if they are taken regularly or not, …
It doesn’t say anything about life quality. For myself (but it might be due to my 55kg) if I don’t eat enough or didn’t eat since too long, I feel tired, harder to focus, … (minor hypoglycemia, likely). I would be interested in seeing cognitive performances evaluation for someone eating “normally” and doing calorie restriction, for example. The brain is a massive calorie burner.
The difference is not so much in the metabolism as in what “as much as they want” means. When people eat ad libitum (which is a fancy way of saying “as much as they want,” ) they vary quite a lot in their caloric intake. Some people engage in mild caloric restriction naturally and some don’t. Of course my discussion assumes that one has conscious control over one’s food intake. So “as much as they want” doesn’t really enter the picture.
Re-read . . I pointed out that I have a basic daily diet—not only is it reasonably consistent in terms of calories, it is also reasonably well balanced and consistent in terms of macro-nutrients. I use calorie counts to make fine adjustments.
I do say a little about it, but the calorie restriction I engage in doesn’t have much effect on my quality of life. That’s not totally true since I like being thin. On the other hand I don’t like denying myself pizza and nachos every day.
Well what kind of calorie restriction are you talking about—mild, moderate, severe, or something else?
Not so sure about that. Comparing how much I eat with how much other people eat, and I would say I eat more than most of them. On the other hand (and much less anecdotal), there has been recent studies showing link between obesity and the kind of gut bacteria someone has.
Everything :) Ideally, we would have many test subjects, measure their cognitive performances initially, make them follow different kind of “calorie restriction” (none, mild, moderate, severe) for weeks or months, and then measure again their cognitive performances, and see if there is a variation.
Unless you watch really carefully, it’s just about impossible to know that. When these types of claims are studied formally or informally, what normally comes out is that (1) what matters is the amount of food consumed; (2) fat people have basal metabolisms which are at least as fast as those of thin people and usual higher; and (3) people are very bad at reporting the amount of food they eat.
But again, I doubt it really matters for the sake of my argument. Whether you have a high metabolism or a low metabolism, it’s probably a good idea to engage in mild caloric restriction; moderate caloric restriction is more iffy; and severe caloric restriction is more iffy still.
Even if you have one of these claimed slow metabolisms, you can easily avoid gaining weight by restricting what you eat. Assuming of course that you are able to control what you eat. If you are unable to control what you eat, then calorie restriction is pretty much an academic issue.
For reasons expressed elsewhere, I am extremely skeptical of what you are implying here. But for purposes of this discussion, it’s a moot point. If you are able to control what you eat, then not being obese is a simple and easy decision. If you are unable to control what you eat (and a lot of people have this problem), then the issue of calorie restriction is premature.
Yes I agree. For what it may be worth, I have been moderately calorie restricted for well over a year now; I have a cognitively demanding job; and I haven’t notice much of a difference. Though I think I am slightly more irritable and impatient.