Since time immemorial, limited-calorie dieting (paired with long distance running) has been the top prescription for weight loss. I myself recommended this strategy during my early years as a “fitness guy” (or whatever I am). Sadly, like so many others, I was giving poor advice. Merely advising the reduction of calorie intake is, in fact, pretty poor advice. While the title of this post is an exaggeration (imagine that), calorie numbers are not what you should be thinking about when think “good nutrition.”
What’s A Calorie?
A calorie is a unit of energy. The body uses the substances in food as fuel for cellular activity, so the calorie value of a food is the total amount of energy your body could obtain from a food. As discussed previously, the three “fuel” sources for the body that make up this calorie value are fat, protein, and carbohydrates. Fat contains 9 calories of energy per gram, while carbohydrates and proteins contain 4.
“Calories In vs Calories Out”
This phrase, the mantra of dietitians everywhere, has lead legions of people to meticulously count the calories they consume every day in order to hit a (generally quite low) number. The idea behind this philosophy is that you expend a certain number of calories every day (depending on your activity level and base metabolism), and if you consume fewer than that number, the remaining expenditure must come from stored calories (mostly stored as body fat). Dietitians like to call this state “negative energy balance.” Consume fewer calories than you expend, and you will lose weight. Likewise, consume more calories than you expend, and you will gain weight (positive energy balance). This idea seems very logical, one reason it has persisted so long. In some ways, it is correct. Unfortunately, it is also very misleading.
The Illusion Of Causation
“Consume fewer calories than you expend, and you will lose weight” implies causation. Eating fewer calories than you expend causes you to lose weight. Unfortunately, the true relationship here is more more correlational than causal. Yes, a negative energy balance is correlated with decreasing body weight, just like increased increased ice cream consumption is correlated with increased incidence of drownings. Does that make the relationship causal? No. In fact, in both correlations, the relationship is due to an external cause. Increased ice cream consumption and increased drownings are both caused by increased outdoor temperature – summer! So what is it that causes the correlation between changes in weight and calorie consumption?
The Common Cause – Hormones
Imagine Yao Ming. He is very tall. To grow as large as he did, he had to consume a lot more calories than I had to consume to grow to a whopping height of 5 feet 10 inches. Does that mean his incredible height was caused by the fact that his mother fed him 5000 calories per day during his growth spurt? Of course not. During the periods of his growth, his body secreted hormones (like growth hormone) which signaled his body to grow and to feed itself adequately for that growth. He was growing; he was hungry; he ate a lot of calories.
A similar causal chain exists with the growth of fat stores in the body. “Storage” hormones, like insulin, signal the body to store nutrients in fat (as well as the liver and muscles). Higher than normal production of insulin results in higher than normal nutrient storage (mostly as body fat) as well as higher than normal consumption. The major difference between the height scenario and the body fat scenario is that what you eat affects the status of your storage hormones. Unlike the hormones which cause vertical growth, over which you have no control, the hormones which result in increased fat storage are impacted to a great degree by what you eat.
A full discussion of insulin would make this post extremely long, so for a full discussion, check out my primer on insulin. For our purposes, a quick summary will suffice. When you eat, food gets digested and nutrients are absorbed into your blood stream. Insulin and other storage hormones are released to shuttle these nutrients into cells for use as fuels. Insulin in particular is released in response to increased blood sugar (glucose). The higher the sugar levels in the blood, the more insulin is released. It follows then, that foods (and entire diets) which cause high blood sugar levels will result in high insulin levels. What do you get with excessive insulin levels? Excessive nutrient storage and excessive consumption.
Back To Calories
So, fundamentally, our thinking about calories is a bit backwards. Yes, we should be conscious of what we put in our bodies. However, more important than the pure number of calories in a given food or meal is the nutrient composition of the food and how it will affect blood sugar and insulin levels. Eating a diet high in simple carbohydrates (like sugars, bread, pasta, rice, flour, and other grain products) will generally result in chronically high insulin levels, leading to increased storage and consumption – more body fat! Eating a diet like the one outlined in my Nutritional Habits will help control insulin levels, generally resulting in more controlled consumption and storage.
In the end, it’s more about what you eat than purely how much you eat. Eat a diet of mostly lean protein, vegetables, and some fruit and you will have a very hard time overeating! No counting required.
For more information on this topic, check out the book Good Calories, Bad Calories by Gary Taubes. It’s a mammoth discussion of this issue, as well as the history of misinformation in the nutritional space regarding calories, fats, and carbs. It’s a fantastic read (although a bit dry) which truly changed my outlook on many things nutritional.