There probably isn’t a topic in nutrition that’s more tangled up in misinformation than calories, so let’s blow up some of those myths.
Sometimes I wish Wilburn Olin Atwater hadn’t become a pioneer in the field of nutrition. I’d have been happier if he’d instead become a chimney sweep, corset maker, rag picker, or some other respectable late 19th-century profession.
Atwater was the guy who figured out the calorie counts of the macronutrients, in addition to cataloging the calorie counts of around 4,000 foods common at the time. He built this room about the size of an old-time telephone booth – called the “respiratory calorimeter” – in which he confined subjects for up to five days while measuring the input of food and oxygen and the output of carbon dioxide, urea, ammonia, and feces, all of which he’d use to calculate caloric intake.
It was so complicated that it took up to 16 people to read all the dials and do the math.
Since Atwater, or anybody else for that matter, didn’t know about vitamins or minerals back then, he incorrectly rated certain foods as superior to other foods. For instance, he gave short shrift to fruits and vegetables while overvaluing meat and, get this, alcohol, since it was high in caloric energy.
Those were probably the first myths in a long line of myths concerning calories that have since been born. Sometimes I think we’d all have better off if, instead of calorie counts appearing on food labels, we simply used a “traffic light” approach: green means eat the food with impunity, yellow means moderation, and red means don’t put that f-ing stuff in your mouth unless it’s some sort of holiday.
Anyhow, here are some of those calorie myths that have spawned since Atwater’s time:
A great many calorie counts on labels are horsepucky. The Food and Drug Administration allows for a 20% “margin of allowance” on such labels, which means a food that’s listed as having 400 calories could have as many as 500 and still be in compliance with the law.
To be fair, the journal “Obesity” tested a sampling of popular common snack foods and found that the actual calorie counts were only 4.3% higher (1) than what the label stated, but personally, that doesn’t give me much solace about the whole calorie disparity issue.
After all, anybody eating snack foods probably doesn’t care so much about the exact number of calories contained in their polypropylene bags of Cheetos. They probably think the numbers on the nutrition label are like the fortune cookies that list lottery numbers.
It’s the possible caloric disparity in healthy/healthier foods that gives me pause. Of course, that’s all the more reason to try and stick with unprocessed foods where you pretty much know what you’re getting. After all, it’s much harder to fudge the calorie count of a cup of oatmeal or a 4-ounce pork chop.
The calorie counts of all modern foods are determined by burning them in something Atwater would have killed to have: the “bomb calorimeter.” It looks like a generic, stripped-down Instant Pot or something they store your brain in after you die for future transplantation into a robotic worker drone.
The thing is a box or cylinder with two chambers, one inside the other. The outer chamber is filled with cold water, and when the food in the bomb calorimeter is burned, an observer records the rise in temperature of the water. If the temp of water goes up 1 degree per kilogram, the food has 1 calorie. If it goes up 2 degrees, it has 2 calories. You get the idea.
The bomb calorimeter is very accurate (when actually used to determine calorie content of foods). The trouble is, our stomachs aren’t bomb calorimeters. We don’t incinerate foods, we DIGEST them, and the efficiency of said digestion is multi-factorial, the result being that we probably absorb about 90% of the caloric energy from the food we eat.
Some Dutch researchers weighed and analyzed the stools of 25 volunteers and found the following (3):
- Total calories absorbed from food: 89.4%
- Total calories absorbed specifically from fat: 92.5%
- Total calories absorbed specifically from protein: 86.9%
- Total calories absorbed specifically from carbohydrates: 87.3%
Perhaps surprisingly, women absorbed even fewer calories from food compared to men – an average of 88% versus 91.8%. They also exhibited a “trend” towards less absorption of fat and carbohydrates than men, but it didn’t reach statistical significance.
If these findings are accurate and also representative of populations other than Dutch people, it makes you wonder about the veracity of most of the other diet and calorie studies done in the last 50 years. Would an absorption rate of 90% instead of 95% skew the conclusions of many past studies? It seems likely.
Certain foods are stubbornly resistant to digestion (4). Take almonds, for instance. The label indicates that an ounce has 168 calories, but digestion studies indicate that the average human absorbs only 129 of those calories. Same for cashews. An ounce is 137 calories instead of the 163 on the label. Pistachios and walnuts too.
It likely has to do with the sturdy cell structure of the nuts’ cell walls. Despite pulverizing them with our molars, a large amount of the cells remain undisturbed, thus protecting them from digestive juices, digestive microbes, and subsequent assimilation. Pulses (grain legumes such as dry peas, beans, and lentils) might be somewhat similarly difficult to digest, thus affecting their ultimate caloric value, too.
Then there’s the way food is cooked. The more you cook, say, a sweet potato, the more of its calories you “release.” When mice were fed raw sweet potatoes, they lost weight, but when they were fed the same amount of cooked sweet potatoes, they gained weight.
Moreover, no two sweet potatoes (or no two examples of practically any fruit or vegetable) will have the same number of calories because they grew in different conditions and were likely cooked in slight but ultimately significant different conditions.
It’s the same with meat. Mice fed raw meat lost two grams of body weight, but mice fed cooked meat only lost 1 gram. Cooking the meat denatures the proteins and makes it easier to digest.
Then there’s resistant starches, those foods whose molecular structure was changed – made more difficult to digest – by how the food was prepared or stored. Bread that is frozen and then toasted donates far fewer calories to the digestive system, as does rice or pasta that’s been cooked, allowed to cool for several hours, and then reheated. (More info here.)
Lastly, there’s the ultimate freer-upper of calories – industrial processing. The more a food is macerated, the more it’s pulverized, boiled, baked, and formed into little animal shapes, the less work the body has to do to assimilate its inherent energy.
Eating a lot of protein, even up to 5.5 times the recommended daily allowance, will not make you gain any additional fat, even if all that protein adds a ton of calories to your diet. Instead, it seems to have a protective effect against fat during periods of increased energy intake while also leading to additional muscle mass, provided circumstances are right.
Dr. Joey Antonio, a contributor to T Nation, set about to “determine the effects of a very high protein diet (4.4 g/kg/d) on body composition in resistance-trained men and women” (9).
The study design was simple: Thirty healthy weightlifting men and women were randomly assigned to a control (CON) group or a high protein (HP) group. The CON group was instructed to maintain their same training and dietary habits over an 8-week period.
The HP group was also instructed to maintain their same training and dietary habits (i.e., maintain the same carb and fat intake), albeit with the added instruction to take in 4.4 grams of protein per kilogram of body weight (about 5.5 times the RDA).
The math shows that the HP group would be ingesting around 800 calories per day more than the CON group. These additional calories were all from protein: 307 +/-69 grams of it, compared to a protein intake of 138 +/- 42 grams in the CON group.
Here’s the clincher: After 8 weeks, despite eating about 800 extra calories per day – all of it from protein – the HP group experienced no changes in body weight, fat mass, or fat-free mass. Great, but you may be raising an eyebrow over the fact that the participants didn’t gain any muscle mass, either. Not to worry. Antonio explained it this way:
“The lack of body composition changes in our group may be attributed to the fact that it’s very difficult for trained subjects to gain lean body mass and body weight in general without significant changes in their training program.”
So, it appears that the HP group simply wasn’t hitting it hard enough.
Bottom line: Protein can turn into body fat, but it’s unlikely. Biochemically, turning dietary fat into body fat is, as you might guess, easy-peasy, and turning dietary carbohydrate into body fat isn’t that much more difficult.
Turning protein into body fat, however, is an entirely different type of challenge. It takes several biochemical and hormonal steps and it’s monitored closely by the liver, which metes out amino acids according to the body’s metabolic needs (tissue breakdown, tissue synthesis, catabolism, anabolism, etc.).
As such, you can believe, with a high degree of certainty, that protein, despite what “common sense” might suggest, has a protective effect against fat gain in times of caloric surplus, particularly when combined with lifting.
Scientists fed a cohort of healthy men a single meal of bread, jam, and fruit juice that totaled 480 grams of carbohydrate (about 1,900 calories), about 8 grams of fat (about 70 calories), and a smattering of protein (12). The scientists then tracked their metabolic responses for 10 hours.
The bulk of the carbohydrate was converted into glycogen (346 grams) while the other approximate 133 grams was burned as fuel. It’s true that their bodies converted some of the carbs to fat through a process called de novo lipogenesis (DNL), but it was only a measly 2 grams. Hear that? A measly 2 grams.
Even better, though, was that during the 10-hour follow-up, the subjects burned 17 grams of fat. That’s 7 grams more fat than the combined total of what was in the meal (8 grams) and the fat they manufactured through DNL (2 grams), so they burned an additional 7 grams of body fat after the meal. So, the gross overfeed led to zero net fat accrual.
Another study soaked their subjects with carbs for multiple days. Healthy young adults consumed 150% of their daily caloric requirements for five days straight, but the extra 50% of calories came purely from carbs (684 grams, or 2,736 extra calories per day).
The amount of fat manufactured (through DNL) by this practice was 10 times what you’d have seen if the subjects were on a maintenance diet, but it still only amounted to gaining 5 grams a day.
That means that five days of pigging out only led to a gain of 25 total grams of fat, or approximately one-eighteenth of a pound of fat. That’s an amount so small that it probably wouldn’t even cause an anorexic to blink.
Make no mistake, you do gain weight after a piggy meal, but as stressed by researcher Alex Leaf, the added weight is unlikely to be fat or at least any substantial amount of fat, especially if the meal (or meals) is a rare occurrence or limited to a short period (like a one-week vacation).
In more concrete terms, you could gain a pound of fat if you eat an extra 500 to 1000 calories a day for a week, but not if you eat an extra 500 or 1000 calories in a single meal. For one thing, there’s a limit to how much food your body can turn into fat (via DNL) in one sitting.
That’s because several things happen when you eat the equivalent of all the foods from column A off a Chinese restaurant menu. Much of it’s stored as glycogen in the liver and muscles, and along with each gram of stored carbohydrate comes about 3 grams of water.
The amount of glycogen stored varies enormously from one individual to another and may be particularly large in lifters, athletes, or muscular people in general, especially if they’ve worked out that day (thus depleting glycogen to a certain degree).
Then there’s the effect the food itself has on the body. Eat a bunch of food and your body temp goes up as it struggles to process it (diet-induced thermogenesis). (Protein is the most “expensive” to metabolize, whereas fat is the least expensive.)
Some of it’s also burned up from NEAT, or non-exercise activity thermogenesis, which is the energy we expend for everything that’s not sleeping, eating, dancing, or doing sports – things like walking, typing, performing yard work, and even fidgeting.
The rest of the actual weight gain is heavily influenced by the amount of sodium and water in the meal, both of which affect blood volume, and then there’s the actual weight of the food that’s slogging through your digestive tract. Most of that “gained” weight doesn’t stick around, though.
It’s an almost universally agreed upon fact that you have to reduce caloric intake 3500 calories below baseline to lose a pound of fat. We know this because, back in 1958, a guy named Max Wishnofsky burned a pound of fat in, yep, a bomb calorimeter and saw that it gave up about 3500 kilocalories’ worth of energy.
And we all swallowed it, hook, line, and pork rind without realizing, again, that we’re not bomb calorimeters and that, moreover, weight loss is governed by a slightly more complex mathematical formula and doesn’t continue in a linear fashion.
It took a mathematician by the name of Kevin Hall, Ph.D., to figure out that over the course of the first year of a diet, people only lose about half of what’s predicted (13). In effect, the true number of calories it takes to burn a pound of fat works out to be closer to 7,000.
Before you scream in anger and frustration, consider what Hall said:
“I suppose some people will be bummed out, but we believe it’s better to have an accurate assessment of what you might lose. That way, you don’t feel like a failure if you don’t reach your goal.”
The main problem with the 3500-calorie rule was it failed to take into consideration that the body pivots and adapts in several ways to minimize or even erase the effects of reduced caloric intake. It doesn’t account for gender, either, or the fact that the metabolic rate drops as body weight decreases.
It also doesn’t take into consideration that counting calories is, for the reasons I laid out above, a woefully inexact science.
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- Cardona-Alvarado MI et al. Almonds and Walnuts Consumption Modifies PUFAs Profiles and Improves Metabolic Inflammation Beyond the Impact of Anthropometric Measure. The Open Nutrition Journal. 2018 Oct;12(1):89-98.
- Acheson KJ et al. Glycogen synthesis versus lipogenesis after a 500-gram carbohydrate meal in man. Metabolism. 1982 Dec 31(12):1234-40. PubMed.
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- Dunn R. The Hidden Truths Behind Calories. Scientific American. August 27, 2012.
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- Antonio J et al. The effects of consuming a high protein diet (4.4 g/kg/d) on body composition in resistance-trained individuals. J Int Soc Sports Nutr. 2014 May 12;11:19. PubMed.
- Leaf A et al. The Effects of Overfeeding on Body Composition: The Role of Macronutrient Composition – A Narrative Review. Int J Exerc Sci. 2017;10(8):1275-1296. PMC.
- Bray GA et al. Effect of protein overfeeding on energy expenditure measured in a metabolic chamber. Am J Clin Nutr. 2015;101(3):496-505. PubMed.
- Leaf A et al. Can one binge make you fat? Examine.
- Webb D. Farewell to the 3500-Calorie Rule. Today’s Dietitian. 26(11):36.