Weight Control, Healthy Food and Counting Calories

Now that we know calories inside out, eating right isn’t about ticking off boxes or gathering random food lists from the web any longer. It’s about using our newfound scientific insights to make smart choices. So what would be the best diet for weight control?

Weight is a measure of your body’s mass. Mass enters the body in the form of food and water. Some of it goes out as excrement. Others are retained to make and repair body parts. Everything beyond that is metabolized to fuel, which is either burned for energy or consigned to storage. Excessive weight comes from excessive body mass for energy storage. Losing weight happens when your body is using up more energy than it’s taking in, and you end up breathing out the excess mass as carbon dioxide and sweating or peeing it out as water. There is no secret formula or magic food: any diet that results in an energy deficit leads to weight loss.

But that’s about as useful as “eat less, exercise more.” It’s easier said than done, and it doesn’t really tell you exactly what to do. Let’s try to get a little more specific and practical.

First, what should we actually eat? Should we cut out meat, fat, carbs, or acidic food? The history of diet science is littered with the hubris of overconfident people who claim to know the exact makeup of a healthy diet. But unless prescribed by a doctor for medical reasons, any diet that limits the kinds of food you can eat is a bad idea. We need more variety, not less, in our food. We evolved to be omnivores. Homo sapiens are the only surviving species of the Homo genus probably because our ancestors could eat a bigger variety of food.

If we don’t eat meat, we may have a hard time getting the right amount of all the essential amino acids and certain vitamins that are common in animal products. Eliminating fat will deprive us of essential fatty acids. Fats play a pivotal role within the physiological framework. They make up cell membranes and the protective coating around our nerve cells called myelin. Some vitamins only dissolve in fat, so without fat, the body cannot retain them.

If we limit carb intake, the Krebs cycle slows down, fat oxidation becomes less efficient, and you will have a harder time participating in endurance sports. The liver also has to work overtime to make glucose. But why is the blood glucose level so important? For starters, our brains really like using glucose for energy. Studies show that after three days of strict fasting, the brain still gets 75% of its fuel from glucose. At least the brain can use ketone bodies in a pinch, but red blood cells can only use glucose for energy. There is a perfectly logical explanation: For mitochondria to produce energy with the Krebs cycle, they have to consume oxygen. But the job of red blood cells is to transport oxygen. They shouldn’t steal the cargo. That’s why red blood cells don’t even have mitochondria, and glycolysis is the only source of energy for them.

When you go on a low-carb diet, you might notice you lose weight pretty quickly at first. That’s because the glycogen store is being depleted. Glycogen is paired with water when it’s stored (technically, it’s a polysaccharide with a lot of hydroxyl groups, which make it hydrophilic). One gram of glycogen holds on to three grams of water. The initial phase of weight loss is largely due to the expulsion of water, a transient effect given the finite glycogen stores within the body.

The trick is adding to the variety while controlling the total input. Why do we often end up eating too much? Throughout human history, starvation was a perpetual threat. Our bodies have developed a sophisticated arsenal of protective mechanisms to guard against hunger. When we are not getting enough to eat, all kinds of alarm bells go off, and various energy preservation processes get going. On the flip side, having too much food is a relatively new problem in the history of human evolution. Even though we now know obesity is unhealthy, our genes haven’t quite caught up with the modern abundance of calories. Our bodies still enthusiastically stockpile surplus energy. We cannot count on our physiology to prevent overeating. The best defense is food that makes you feel full and keeps you feeling full.

Satiety is an important measure of food quality that often gets overlooked. All food gives us calories, but not all calories are created equal. Low-quality calories come from foods that have a lot of them, but have little else and don’t keep you feeling full. Now we can see the problem with refined carbohydrates like white rice: it consists almost entirely of easily digested starch, which leaves your stomach quickly and gets absorbed in no time. It’s the same with sugary drinks—they’re packed with what we call “empty” calories. If you are watching your weight, a good rule to follow is to never drink your calories.

In contrast, protein takes 2 to 4 hours to empty out of the stomach. It is harder to digest and travels further down your gut. Remember our discussion about Ozempic? Less digested food reaching the latter part of the intestine triggers the “I am full” signal. Digested proteins also elevate the amino acid and ketone levels in the blood. Consequently, a calorie from protein possesses a greater satiety value than one from carbohydrates. Another advantage of protein as a calorie source is that it incurs a higher cost of metabolization (the diet-induced thermogenesis in Figure 1). So protein’s net metabolizable energy is less.

As in the case of calories, you should be mindful of what else is in the food besides protein. It could be antibiotics and growth hormones from questionable meat or fiber and omega-3 fatty acids from avocados. Food quality should be considered in the whole food context.

Finally, for an article titled “The Science of Counting Calories,” we have to address this question: should we count calories? Science cannot answer questions that begin with “should” because it implies a value judgment, and everyone has different values. But as a practical matter, my answer is: Probably not