Does it matter where we get our energy from? “A calorie is a calorie”, many experts say, and the food industry has been happily endorsing that mantra for decades. Doesn’t matter whether you are eating broccoli, chocolate, bread or beef … it’s all just calories. Or is it?
No. You know that what you eat has huge implications. Why else would we be so particular about the foods we eat? The body is a biochemical laboratory, constantly metabolizing (burning) food for energy. The metabolic pathways for our major energy-yielding macro-nutrients (fat, carbohydrate and protein) are very different. When you eat 1,000 calories of either sugar or fat, while the amount of energy is the same, different chemicals are produced while metabolizing the food, and different configurations of various hormones and enzymes ensue.
Since of the three macro-nutrients protein is primarily used as building material, we can focus on the two remaining macronutrients, fat and carbohydrate. We are left with three basic strategies:
Fat Based Diet (Low-Carb)
This is the primal/keto/carnivore approach. The body optimizes its metabolic pathways for burning fat, including the production of ketones. This strategy is well suited for body-fat loss and lean body maintenance. People on this diet will tend to eat fewer meals, since the body is used to accessing its fat stores efficiently when there is no food “coming in”.
Typical meal options using whole foods: Steak/fish/eggs and vegetables/low-sugar fruit.
Carb Based Diet (Low-Fat)
This is the typical plant-based/vegan approach. Little or no meat is consumed, or at best only lean meat, and as little fat as possible. While this is certainly compatible with optimizing body composition, it is more difficult to maintain for most people, and prone to developing deficiencies. On this diet people will gravitate towards eating more frequently throughout the day, since the body is not used to burning fat efficiently. As soon as the carbs from the last meal are used up, without ketones in the system to fuel the brain it senses an energy crisis, prompting its “user” to eat again.
Typical meal options using whole foods: Salad with low-fat dressing and bread, oatmeal, cereal, fruit salads or smoothies.
The ”Balanced” Diet (Moderate-Fat, Moderate-Carbs)
This is the standard “Western” Diet. While some people might be able to stay lean on a “balanced” mix of carbs and fat, most people will find it difficult not to overeat calories, since mixing carbs and fat not only maximizes the energy content of food, but also makes them hyper-palatable. Some research also hints towards unfavorable effects on blood lipids when saturated fats are consumed in a high-carb setting.
Typical meal options using processed foods: Burgers and chips/fries, pasta and cheese, donuts, cakes, ice cream, pizza, chocolate, peanut butter and jelly sandwich
Typical meal options using whole foods: Fatty meat/fish/eggs and (sweet) potatoes, nuts and (dried) fruit
So are carbs evil?
Yes, if you eat them with a lot of fat.
So is fat evil?
Yes, if you eat it with a lot of carbs.
But saturated fat is surely always evil?
No. When you eat saturated fat, what happens to it depends heavily on two factors: whether you are overeating, and the presence of carbs. If you are not overeating and few carbs are present, the saturated fat you eat will swiftly be burned for energy by the body, no harm done. On the other hand, when you overeat and mix saturated fat and carbs, it may linger in the blood stream and cause undesirable effects. So: Steak and butter is ok, but not if you add a big baked potato.
Isn’t it enough to cut out sugar?
No. Granted, a no-sugar diet avoids many bad foods. But if it still contains carbs and fat, the body is probably still confused. The food sends mixed signals. Carbs are like rocket fuel for the body. Even complex starches are eventually broken down to glucose, which must be burned for energy immediately. Simultaneously you are giving the body slow-burning fat.
So what do I do if I currently eat a 50:50 diet?
The worst you could do would be to eat more fat on top. Fat is healthy only if you make it the main source of energy in the diet by simultaneously cutting out carbs. The second worst thing you could do is to eat more “healthy” carbs on top. The key is to pick one major source of calories – either fat or carbs – and then to implement your diet using foods rich in protein and micro-nutrients.
How does this principle of not mixing fat and carbs align with evolution?
Quite well! Think about the kind of foods which were available to humans hundreds of thousands of years ago: Whole plants and animals, basically. What do all of them have in common?
None of them are mixtures of fat and carbs. Most plants contain almost exclusively carbohydrate, except for nuts, seeds and some special types of fruit like avocados and olives, which contain predominantly fat. Meat, fish, eggs and other animal foods are basically protein and fat without any carbohydrate. Milk is an exception, since it contains a mix of carbs and fat. It exists specifically for the purpose of supporting growing babies, so it is the one whole food that is not appropriate for our purposes. But that is in line with evolution, since humans have been eating milk for a very short time, even today there are many populations which are predominantly lactose intolerant. We can still eat high-fat or high-protein dairy though, in which the lactose has been largely removed.
So does that mean that I have to be either carnivore or vegan?
No. Granted, fat and meat are a natural match, as are carbs and plants. But it is possible to do a fat-based vegan diet, based largely on nuts, coconut, olives and avocados. The other extreme, a carbs-based carnivore diet, is of course not possible. Maybe if you ate only skim milk and whey protein … which is hardly sustainable.
Of course various combinations of animal and plant foods are possible. Fatty meat and vegetables is very popular, on the carbs-heavy side one could eat lean meat, vegetables and pasta or rice, which is the basic blueprint of “clean eating”.
With the focus on fat vs. carbs, is protein irrelevant?
Not at all. In fact, protein is absolutely crucial. In order to thrive, we have to continuously eat at least as much protein as the body is breaking down. On a fat-based diet we need to eat even more protein, since the body uses some of it to generate glucose through a process called gluconeogenesis. Age is also a factor: the older we are, the more protein we should eat, since the body breaks down more tissue and struggles more to replace it.
One useful rule of thumb is to eat at least 2 grams of protein per kg of your ideal body weight each day.
Ha! Gotcha! Why not just eat the carbs rather than getting them via gluconeogenesis?
Not so fast. Remember that the context for gluconeogenesis is a fat-based diet. Such a diet works only well when the body can burn its fat stores efficiently. In order for that to happen, carbohydrate intake needs to be very low. This causes insulin levels to drop, and glucagon levels to rise. And only this rise in glucagon enables the liver to produce ketones and fine-tune blood sugar by producing glucose from protein exactly when needed, and in the amounts required.
But glucose is the preferred fuel for the body!
Yes and no. Yes, the body preferentially burns glucose rather than fat. But why? Maybe another nutrient serves as a good illustration: alcohol. Turns out that the body burns alcohol even before glucose. Does that mean that we are meant to run on alcohol? No, it means that alcohol is a poison, and the body tries to get rid of it as fast as possible. It is similar with glucose. It is a poison if present for too long, and in high concentrations.
“Preferred” is not a good criterion for choosing what to eat. We should rather ask ourselves which macronutrient our body uses to store energy. That is the energy source our body uses as a default when we, for whatever reason, don’t eat for a while. And this default fuel, fat, is what we should probably prefer to eat.
In the end, which is superior – fat or carbs?
That depends on who you ask. The jury is still out. But having tried both, I prefer the fat-based approach. The big drawback is the social pressure you face for not eating carbs and skipping meals. But the improved satiety and digestion are huge advantages. If you add exercise to the mix, you can get away with some transgressions – for me mainly chocolate and fruit, occasionally. I gave the plant/carbs based approach a chance a few months ago, but I finally gave up. I actually like the foods a lot – muesli, plant milks, fruit, beans, bread, whole-wheat pasta, tomatoes … taste-wise it was not a problem at all. Digestion was horrible though, and I felt hungry all the time. On the other hand, when I eat mostly meat everything is easy and awesome without much optimization at all.