Food we eat is broken down into 3 main macronutrients; carbohydrates, dietary fats, and protein. I hope I don't have to get into the discussion about why all 3 macronutrients are important for the human body and that one macronutrient doesn't necessarily make you any fatter than the other 2. Let's just clear the air now and discuss the fact that an over-consumption of calories is what leads to weight gain, not necessarily where those calories are coming from. We will discuss this as we go.
Carbs (sugar) are the easiest macronurtient to digest and therefore has the highest net energy yield. Carbs are nature's form of jet fuel for our bodies. The problem is, our society seems to pack more and more and more sugar into everything, leading us to the point where we would never come close to burning off as much of that energy as we take in, leading to adipose tissue (body fat). Anyways, carbs return about a 90-95% energy yield per calorie. What I mean by that is, every 100 calories of carbs you take in, it requires just 5-10 calories of energy to digest.
Carbohydrates do not make you fat, an excess of sugar and calories make you fat or gain weight. I always recommend people track their diet, even for a short-term period because oftentimes they are surprised by just how much sugar they are consuming on a daily basis. Beverages can be a very big culprit for this. Don't drink your calories if your goal is to lose weight, stick to water, tea or coffee.
Fats actually have a slightly higher energy yield than carbs, ranging in the ballpark of 95-96%, but this should not be alarming as our diets require much less fat than carbs. What this means is that in 100 calories of fat, it takes about 4-5 calories to digest. Keep in mind that dietary fats can be extremely beneficial to the human body and are a great way to give you a feeling of satiation (feeling "full).
Dietary fats do not make you fat, an excess of dietary fats make you fat. Due to their extremely high nutrient density (over twice as calorically dense as both carbs and protein), their calories add up quickly in less overall quantity, so being aware of how much fat you are consuming is important to effective weight management. Dietary fats are great for a lot of things such as building cell walls, producing hormones (testosterone, anyone?), transporting vitamins through your body, but can push your caloric intake high, so watch out for things like creamy sauces if you're trying to lose weight as they tend to be caloric bombs.
Protein has the lowest energy yield, which can actually be very beneficial for weight loss. Only about 70-80% of protein calories consumed are returned to the body, which isn't all that surprising as the body greatly prefers fats and carbs for energy whereas protein is mostly used for tissue repair and remodelling. This is also why protein tends to be an effective macronutrient in the battle against body fat and weight gain. Even though it is entirely possible to get fat from eating too much protein (too many overall calories), by enriching your diet with protein helps keep you full, makes sure your body is repairing itself from exercise effectively, but also has the lowest caloric yield.
If you are active and are exercising regularly (including resistance training, right?), then you should aim for about 1g of protein per pound of body weight. As it turns out, when you consume your protein doesn't really matter, it also doesn't matter how much protein you eat at one time. As long as you are consuming a set amount of protein between the time you wake up until the time you go to bed, then you should be just fine in meeting your needs for the day.
When you eat your food, your teeth chew it up, then the juices in your stomach break things down further into a paste. This paste then travels through your intestines where the nutrients are absorbed through the spongy walls. For most people, however, 5-10% of this paste just keeps passing on through and is expelled as waste.
For the most part, fat digests easily and passes through the walls quickly. Animal protein sources are absorbed better than plant-based sources. Then we come to carbs. Sugary and starchy carbs are absorbed rapidly, whereas high-fiber carbs like in fruits, vegetables and grains take their time passing through your system. Not only that, but fiber seems to prevent your body from absorbing certain calories and can even lower cholesterol levels. An equal amount of broccoli and chocolate (comparing calories to calories) does not mean that they act the same way in your body, however. Studies have shown that individuals with high-fiber diets have close to 20% of their daily ingested calories move through their digestive system without being absorbed. Less calories this way can lead to less body fat!
Tyler Robbins B.Sc. CSCS
Director of Fitness
Head of CrossFit