Though the “calorie” issue is one of the most hotly debated topics in the overall health and fitness discussion, there’s actually quite a lot of scientific research on it, enough so that at this point it’s safe to say there’s a decidedly clear answer to the question.
And there’s no reason to beat around the bush: Yes, calories do matter for weight loss (or weight maintenance/gain for that matter).
A Rundown of The Pertinent Science
The easiest way to analyze the calorie hypothesis is by trying to falsify it. If something else besides overall calories influences weight and/or body fat levels – fat, carbs, sugar, number of meals per day, etc. – then we’d expect experiments that manipulate such things while controlling for calories to result in changes in weight and/or body fat levels.
But it appears that the opposite consistently happens – so called “isocaloric” ward based RCTs (meaning the researchers administer and thus control the participants’ food intake) routinely fail to produce any change in weight or body fatness.
A meta analysis published by Hall et al that compared 20 isocaloric RCTs concludes that varying fat or carbohydrate ratios has negligible effects on weight and/or body fatness. (ref)
In his book The Fat Loss Bible, Anthony Colpo found and analyzed 28 isocaloric studies which varied protein, fat, and carbohydrate ratios. The result? 25 out of 28 of these studies found no change in weight. The other three found a *modest* reduction in weight when protein intake was increased. (ref*)
(*note: sourced specifically from Table 1a: Metabolic Ward Trials of Isocaloric Diets Varying in Macronutrient Content)
Regarding the issue of increased protein: The latter 3 of the 28 studies in Colpo’s table 1a, and others, do indeed show that higher protein intake can produce modest weight loss (ref,ref,ref,ref,ref). But, this difference can be accounted for with a fairly straightforward explanation: that protein is about 15% less efficiently metabolized then either fat or carbohydrate. (ref) It’s not that protein is a magic boon of weight loss or “metabolic advantage,” it’s simply that that we can get away with eating maybe 100-300 calories per day more of it since the caloric yield is slightly less. Though a 100-300 calorie differential is certainly not insignificant, it’s not nearly large enough to totally reject the calorie hypothesis.
Further reviews of the literature confirm the calorie hypothesis or fail to falsify it:
- Eating small, frequent meals does not produce weight change either if calories are controlled for. (ref)
- Eating at night, or meal timing in general, does not produce weight change either if calories are control for. (ref)
- Calorie restriction does consistently produce weight/fat loss, regardless of diet type. (ref)
But what about all those other studies where people ate less, and they thus should have lost weight, but didn’t? Or what about so and so who claimed they ate less on fad diet X but didn’t lose weight, or so and so who claimed they ate as much as they wanted on fad diet Y and still lost weight?
Well, it’s notoriously difficult (if not impossible) to glean definitive conclusions from non ward free living studies – or personal anecdotes – because they don’t effectively control for extraneous variables, specifically calories in this case. We simply can’t know if self reported food intake is accurate or not, and indeed, research does show that people tend to underestimate and/or underreport their food intake. (ref)
The extensive evidence via many tens of pertinent studies makes the issue quite clear, and simple: Overall calorie balance is what influences weight loss.
Corroboration via Pertinent Statistics
If we’re now assuming the calorie hypothesis is true, then we’d expect see a strong correlation between obesity rates and calorie intake. And indeed there is one – Dr. Stephan Guyenet fit a graph that compares overall caloric intake with obesity rates in the Unites States from 1970 to 2010, based off of data from the CDC, and indeed the fit is, as he says “extraordinary”:
This longitudinal data is corroborated by an analysis published in the American Journal of Clinical Nutrition which concludes that “increased [overall calorie] supply is more than sufficient to explain the US epidemic of obesity.” (ref) And it isn’t all that surprising when you consider that, according to the USDA, the US Food industry is producing around 4000 calories per person – that’s more than double the amount that most people actually need. (ref**, ref)
**note: see “Nutrient Availability” spreadsheet dated 2/1/15
Consider also that occupational related calorie expenditure has also decreased by around 15% since the 1960s, which is explainable by the fact that “sedentary” jobs have risen by ~30% while non sedentary “manual” jobs have concurrently fallen by ~30%:
The fact that people are expending less calories overtime in conjunction with consuming more calories overtime makes the strongly correlating increase in obesity overtime all the more compelling.
In Conclusion: An Understated Yet Liberating Corollary
Yes, calories do matter for weight/fat loss, but the silver lining is that nothing else really does. In realizing this, one realizes that dieting for weight loss/management can actually be very simple, and flexible to their specific situation.
Many people think that weight loss is prohibitively complicated or involved because they think they need to adhere to complex and strict food selection rules, or to eat “clean,” or to prep healthy snacks every few hours, or to avoid social situations involving nighttime eating, etc.
But, as it turns out, all such restrictions don’t actually make a difference, or they only matter secondarily insofar as they influence overall calorie intake.
Point being: you can effectively control and restrict calories for weight loss – while getting complete nutrition of course – with all kinds of different diets and/or eating schedules. Just about anyone can find a system that’s feasible, and it certainly doesn’t need to be a deary spartan’s diet of plain chicken and steamed broccoli.