What is a calorie, anyways?

Team Maize did not stop to ask questions today; we simply took over MedChef, the most intense competition that medical students go through during the first week of “class.” The winning team used local lake fish, creative chilled couscous, and a brilliant balsamic reduction. It’s embarrassing how excited I am about the oven mitts that we won.

In honor of today’s competition, here we go with the first of many posts about food. (Full disclosure: I am not always proud to be an American.) I find it amusingly ironic that a country with such an obvious obesity problem also has such a disastrous dieting problem. Yes, I do mean a dieting problem. Eating disorders aside, there is an unnatural obsession with finding easy, clear solutions. “Don’t eat this. Walk this many minutes. Drink this tea. Eat that weird berry.” Sadly, these proposals strike me as the typical American response to a problem. Changing our entire lifestyle, of course, is out of the question. We want a plan and we want control.

Of perennial interest in the dieting and obesity research community is the question of whether a calorie is just a calorie (i.e. does 200 calories of soda affect your waistline in the same way as does 200 calories of apple?).

It’s an interesting question and before we even look at the most recent studies I’ll point out a few obvious caveats, using our soda versus apple example.

People who drink soda are probably not about to go exercise, since bubbly stomach is not so fun during a run.

People who drink soda might be people who also snack on salty, fatty food.

Soda drinking is associated with fast food consumption, which negatively correlates with having a family dinner time, so fast food also negatively correlates with having a regular sleeping/eating/exercising schedule.

Apples are fibrous and therefore might prevent further snacking (though are purely carbohydrates and thus cause a spike in blood sugar that comes with a subsequent crash and further cravings…hmmmm, best be paired with almond butter, I suppose).

People who eat apples might live on a farm and do a lot of manual labor (okay, okay, I digress).

Researchers interested in weight loss and weight gain have long been curious about the importance of where the calories come from. There have been bizarre low-carb fads (news flash: your brain runs almost exclusively on glucose, plus raspberries and oatmeal are delicious) and low-fat trends (N.B.: without enough fat in your diet, your hair and skin will be dry and ugly). A recent study published in The Journal of the American Medical Association tried to show that people on a high-fat, high-protein diet (as Atkins once suggested) burned more calories than those on a high carbohydrate diet. Essentially, the study authors Ebbeling et al. suggested the after losing weight people should be reluctant to add too many carbs back into their daily routine. 

Numerous scientists have come out to publicly disagree with the suggestions this study puts forth. The esteemed Dr. Jules Hirsch of Rockefeller University, who has been researching obesity for almost six decades, looks like he knows what he’s talking about.

I am inclined to listen to Hirsch’s simple explanation for why the study came up with misleading results. The experiment went something like this: Ebbeling took a sample of 21 people, forced them to lose 10-20% of their body weight, and then put them on one of three maintenance diets — low-carb/high-fat, high-carb/low-fat or moderate. The study’s outcome measure was total energy expenditure and resting energy expenditure, expressed as calories burned. However, low-carb diets can cause mild to severe dehydration. Water loss confounds attempts to measure energy output because the measurement is usually expressed as calories per unit of lean body mass. Less water means less lean body mass and therefore more calories per unit lean body mass (or so it appears). What has actually happened is that dieters have lost water, not fat.

Besides, who are we kidding? All that matters in terms of weight loss is calories in versus calories out. People who want to lose weight need to take in fewer calories or expend more, or both.

(There are, as always, a few additional complications, such as the fact that muscle weighs so much more than fat, but we will ignore that for the moment. If you are on your way to becoming a body builder, we should talk more about this.)

Additionally, there have been other studies that explicitly studied how people respond to diets of different compositions. Dr. Rudolph Leibel conducted a fascinating study with people of normal weight who were recruited to live in a carefully controlled hospital setting. While keeping each person’s caloric intake – and weight – constant, he changed the proportions of fats and carbohydrates. There were no differences in response found between the high-fat and low-fat diets. His now-classic study did find, though, that people reduced their energy expenditure when their weight was lower than normal and burned calories faster when their weight was higher than normal. In humans, this is one of the ways in which body weight is regulated.

The moral of the story is that there is NOT a magical diet. As some wise people have been saying for years (or millennia), it’s about moderation. Take a look at France, Switzerland, and Italy, for instance. I can assure you that they enjoy their fair share of cheese, chocolate, and wine, and yet a European’s chances of becoming obese are slim (pun intended).

The other moral of the story is that if you live somewhere humid and you like to be active, be sure to have sufficient sugar and salt in your diet to retain some water. It’s not the end of the world; it’s being well-hydrated.

And, to get back to the question posed in this post’s title, a calorie is technically defined as the amount of heat-energy required to raise one gram of water by one degree Celsius. The “calories” you see on food labels are actually kilocalories. In carbohydrates and proteins, you get 4 kilocalories of energy per gram of food, while in fat you get nine. For instance 8 grams of brown sugar gives you 8*4 = 32 calories and 8 grams of olive oil gives you 8*9 = 72 calories. It gets more complicated, obviously, with something like chocolate where you have fat and sugar and protein. I’d say 8 grams chocolate = not enough = minimal satisfaction = lack of satiation.