I read a tremendous number of research papers each week in order to keep up with the rapidly changing field of nutrition, physiology, and all topics related to body recomposition. From time to time, I like to review research papers that I think are interesting to my readers; while these are usually new papers, sometimes, I also go back to older papers that happen to be relevant or important. This week’s paper is one of those older papers that addresses one of the longer-standing myths in the field of weight loss, that of meal frequency.
Bellisle F et. al. Meal frequency and energy balance. Br J Nutr. (1997) 77 (Suppl 1):S57-70.
Several epidemiological studies have observed an inverse relationship between people’s habitual frequency of eating and body weight, leading to the suggestion that a ‘nibbling’ meal pattern may help in the avoidance of obesity. A review of all pertinent studies shows that, although many fail to find any significant relationship, the relationship is consistently inverse in those that do observe a relationship.
However, this finding is highly vulnerable to the probable confounding effects of post hoc changes in dietary patterns as a consequence of weight gain and to dietary under-reporting which undoubtedly invalidates some of the studies
We conclude that the epidemiological evidence is at best very weak, and almost certainly represents an artefact. A detailed review of the possible mechanistic explanations for a metabolic advantage of nibbling meal patterns failed to reveal significant benefits in respect of energy expenditure.
Although some short-term studies suggest that the thermic effect of feeding is higher when an isoenergetic test load is divided into multiple small meals, other studies refute this, and most are neutral. More importantly, studies using whole-body calorimetry and doubly-labelled water to assess total 24 h energy expenditure find no difference between nibbling and gorging. Finally, with the exception of a single study, there is no evidence that weight loss on hypoenergetic regimens is altered by meal frequency. We conclude that any effects of meal pattern on the regulation of body weight are likely to be mediated through effects on the food intake side of the energy balance equation.
Perhaps one of the longest standing dogmas in the weight loss and bodybuilding world is the absolute necessity of eating frequently for various reasons. Specific to weight loss, how many times have you heard something along the lines of “Eating 6 times per day stokes the metabolic fire.” or “You must eat 6 times per day to lose fat effectively.” or “Skipping even one meal per day will slow your metabolic rate and you’ll hoard fat.” Probably a lot
Well, guess what. The idea is primarily based on awful observational studies and direct research (where meal frequency is varied within the context of an identical number of calories under controlled conditions) says that it’s all basically nonsense. The basic premise came, essentially out of a misunderstanding of the thermic effect of food (TEF) also called dietary induced thermogenesis (DIT) which are the calories burned in processing of the food you eat.
While TEF differs for the different nutrients, on average it constitutes about 10% of a typical mixed diet (this varies between nutrients and slight differences may be seen with extreme variations in macronutrient intake). So every time you eat, your metabolic rate goes up a little bit due to TEF
Aha! Eat more frequently and metabolic rate goes up more, right? Because you’re stimulating TEF more often. Well, no. Here’s why:
Say we have two people, both eating the same 3000 calories per day from identical macronutrients. One eats 6 meals of 500 calories/meal while the other eats 3 meals of 1000 calories/meal and we’ll assume a TEF of 10%. So the first will have a TEF of 50 calories (10% of 500) 6 times/day. The second will have a TEF of 100 calories (10% of 1000 calories) 3 times/day. Well, 6X50 = 300 calories/day and 3X100 = 300 calories/day. There’s no difference.
Of course, if you increase food intake from, say, 1500 calories to 2000 calories, you will burn more with TEF; but this has nothing to do with meal frequency per se, it has to do with eating more food. I only bring this up because I’ve seen people (try to) argue the positive effect of TEF by dredging up studies where folks ate more total calories. Of course TEF goes up, but not because they are eating more frequently; rather it’s because they are eating more food in total.
I want to address that last bit a little bit more since the fact that TEF goes up with increasing food intake is often used to argue that “metabolism chases intake” and to make arguments for eating more to get lean. Here’s the problem with this ‘logic’. Assuming an average 10% TEF, increasing food intake from 1500 calories to 2000 calories per day will increase caloric expenditure by 50 calories. But you had to eat 500 more calories to get it. So even if you burn 50 calories more, you’re still consuming 450 more calories than you would have otherwise. Basically, the logic is akin to saying “I saved $100 by spending $1000 because what I bought was 10% off”. Right, but you’re still out $900 that you wouldn’t have spent and you’d have saved $1000 if you hadn’t bought it in the first place. The same logic applies here.
Which brings me, the long way around, to the above review paper which examined not only earlier observational work but also direct studies of varying meal frequency on either weight loss (during such studies) or metabolic rate. And, with the exception of a poorly done study on boxers (which I’ll discuss a bit below), they found no effect of varying meal frequency on any of the examined parameters. No increase in metabolic rate, no increase in weight loss, no nothing. What’s going on?
They concluded that earlier studies finding an effect of meal frequency on weight gain (or loss) had more to do with changes in appetite or food intake, not from a direct impact on metabolic rate. For example, early observational studies found that people who skipped breakfast were heavier and this still resonates today with the idea that skipping breakfast makes you fatter. However, the review points out that this may be confusing cause and effect: people often start skipping meals to lose weight.
I’d note, tangentially and I’ll come back to this below, that there is no data in humans that skipping a single meal or even a day’s worth of meals does anything to metabolic rate. Human metabolism simply doesn’t operate that quickly and various research into both fasting and intermittent fasting show, if anything, a slight (~5% or so) increase in metabolic rate during the initial period of fasting. The idea that skipping breakfast or a single meal slows metabolic rate or induces a starvation response is simply nonsensical.
Basically, there are a lot of confounding issues when you start looking at observational work on diet and body weight. As I discussed in detail in Is A Calorie A Calorie, you often find that certain eating patterns impact on caloric intake. And it’s those changes in caloric intake (rather than the eating patterns themselves) that are causing changes in weight
For example, some early studies actually found that eating more frequently caused weight gain, mainly because the foods being added were snacks and were in addition to normal food intake. In that situation, a higher meal frequency led to greater food intake and weight gain. But it wasn’t the meal frequency per se that caused the weight gain, it was the fact that folks were eating more.
Other studies have shown that splitting one’s daily calories into multiple smaller meals helps to control hunger: people tend to eat less when they split their meals and eat more frequently. But, again, this isn’t an issue of meal frequency per se, it’s because food intake is decreased. When folks eat less, they lose weight and IF a higher meal frequency facilitates that, it will cause weight loss. But, at the risk of being repetitive, it’s not because of effects on metabolic rate or any such thing; it’s because folks ate less and eating less causes weight loss.
I’d note that the above observation isn’t universal and some people report that the simple act of eating makes them hungrier. Many people are finding that an intermittent fasting protocol, where they don’t eat anything for most of the day followed by one or two big meals works far far better for food control than the standard of eating many small meals per day. Again, this isn’t a universal and I’m currently examining differences between people to determine who will respond best to a given pattern.
I’d also note that there is a fair amount of literature that eating more frequently has benefits in terms of blood glucose control, blood lipid levels and other health markers. I’d add to that the recent work on caloric restriction and intermittent fasting (a topic I’ll look at in a later article) is finding massive benefits (especially for the brain) from less frequent meals. So even this topic isn’t as simple as ‘more frequent meals is healthier’.
However, this is all tangential to the claims being made for metabolic rate. Whether you eat 3 meals per day or 6, if your daily caloric intake is identical, you will expend the same number of calories per day from TEF. While work in rats and mice, for whom everything happens faster, has found that a single meal can lower metabolic rate, this is irrelevant to humans. Skipping a meal will not affect human metabolic rate at all.
Quite in fact, it takes at least 3-4 days of fairly strict dieting to impact on metabolic rate (and some work on fasting shows that metabolic rate goes UP acutely during the first 72 hours of fasting); a single meal means nothing. You will not go into ‘starvation mode’ because you went more than 3 hours without a meal. Nor will your muscles fall off as an average sized food meal takes 5-6 hours to fully digest, as I discuss in The Protein Book.
Now, all of the above is only looking at the quantity of weight loss, not the quality. For athletes and dieters, of course, sparing lean body mass and losing fat is a bigger goal than how much weight is actually lost. Which brings me to the boxer study that everybody loves to cite and nobody seems to have read (except me as I spent years tracking down the full text of the paper).
In this study, boxers were given either 2 or 6 meals per day with identical protein and calories and examined for lean body mass lost; the 2 meal per day group lost more lean body mass (note: both groups lost lean body mass, the 2 meal per day group simply lost more). Aha, higher meal frequency spares lean body mass. Well, not exactly.
In that study, boxers were put on low calories and then an inadequate amount of liquid protein was given to both groups and the meals were divided up into 2 or 6 meals. But the study design was pretty crappy and I want to look at a few reasons why I think that.
First and foremost, a 2 vs. 6 meal per day comparison isn’t realistic. As discussed in The Protein Book, a typical whole food meal will only maintain an anabolic state for 5-6 hours, with only 2 meals per day, that’s simply too long between meals and three vs. six meals would have been far more realistic (I would note that the IF’ing folks are doing just fine not eating for 18 hours per day).
Additionally is the use of a liquid protein that confounds things even more. Liquids digest that much more quickly than solid foods so the study was basically set up to fail for the low meal frequency group. They were given an inadequate amount of rapidly digesting liquid protein too infrequently to spare muscle loss. But what if they had been given sufficient amounts of solid protein (e.g. 1.5 g/lb lean body mass) at those same intervals? The results would have been completely different.
As discussed in The Protein Book in some detail, meal frequency only really matters when protein intake is inadequate in the first place. Under those conditions, a higher meal frequency spares lean body mass. But when protein intake is adequate in the first place (and again that usually means 1.5 g/lb lean body mass for lean dieters), meal frequency makes no difference. And that’s why the boxer study is meaningless so far as I’m concerned. An inadequate amount of liquid protein given twice per day is nothing like how folks should be dieting in the first place.
In any case, let me sum up the results of this review: Meal frequency per se has essentially no impact on the magnitude of weight or fat loss except for its effects on food intake. If a high meal frequency makes people eat more, they will gain weight. Because they are eating more. And if a high meal frequency makes people eat less, they will lose weight. Because they are eating less. But it’s got nothing to do with stoking the metabolic fire or affecting metabolic rate on a day to day basis. As the researchers state above:
We conclude that any effects of meal pattern on the regulation of body weight are likely to be mediated through effects on the food intake side of the energy balance equation.
And that’s that.
The take home of this paper should be fairly clear and I’m going to focus primarily on dieting and weight/fat loss here. I’m also going to assume that your protein intake is adequate in the first place; if you’re not getting sufficient protein during your diet, you have bigger problems than meal frequency can solve.
Before summing up, one last thing, from a practical standpoint, I sometimes wonder if the people who are adamant about 6 meals/day have ever worked with a small female athlete or bodybuilder. A 120 lb female may have a daily food intake of 1200 calories/day or less on a diet.
Dividing that into 6 meals gives her 200 calorie ‘meals’. More like a snack. 4 meals of 300 calories or even 3 meals of 400 calories is a much more livable approach than a few bites of food every 3 hours.
By the same token, a very large male with very high caloric requirements (for dieting or mass gaining for example) may find that fewer larger meals are difficult to get down or cause gut discomfort, eating more frequently may be the only way to get sufficient daily calories.
But again, these are all completely tangential to any (non-existent) impacts of meal frequency on metabolic rate or what have you.
So here’s the take home:
- If eating more frequently makes it easier to control/reduce calories, it will help you to lose weight/fat.
- If eating more frequently makes it harder to control/reduce calories, or makes you eat more, you will gain weight.
- If eating less frequently makes it harder for you to control/reduce calories (because you get hungry and binge), it will hurt your efforts to lose weight/fat.
- If eating less frequently makes it easier for you to control/reduce calories (for any number of reasons), then that will help your efforts to lose weight/fat
I personally consider 3-4 meals/day a workable minimum for most, 3 meals plus a couple of snacks works just fine too. High meal frequencies may have benefits under certain conditions but are in no way mandatory. And, in case you missed it the first time through: eating more frequently does NOT, I repeat DOES NOT, ‘stoke the metabolic fire’.