Lately, there has been a lot of press about both ketogenic (keto) and whole food plant based (WFPB) diets. By definition, keto diets are high in (almost always animal) fat and very low in carbs. In almost all cases, WFPB are high carb and low fat. The keto camp says carbs will trigger an insulin response making you store them as fat, while the WFPB side often says, “the fat you eat is the fat you wear.” What are we to make of these claims, and who is the friend or foe?
I am only choosing to look at Keto vs WFPB because these generally represent opposite dietary approaches on a macro-nutrient level. Interestingly, both can succeed in weight loss for most people. To understand this seeming contradiction, it is helpful to understand how the body is fueled and the efficiency of the fueling process.
The preferred fuel of the body is carbs. Using an enzyme called amylase, the body can easily break down carbs into glucose which is used directly for energy. Every cell in your body prefers to use glucose as its energy source because this process is easy and efficient for the body to perform. Despite, glucose being the preferred energy source, the body has a fairly limited capacity to store this fuel, about 500 grams worth. In its stored form, it is called glycogen, and it stored primarily in muscle cells and the liver. When your body runs out of glycogen, it will switch to a back-up fuel from stored fat. As we are all painfully aware in 2019, for many people, there are huge fat reserves available. The process by which the body converts fat into fuel is called ketosis, which is where the “keto” in “ketogenic diet” comes from. Unlike burning carbs as fuel which has byproducts of just carbon dioxide and water, ketosis has a by product of an acid (ketones). There is more stress on the body in using fat as fuel, which is another reason carbs are preferred.
It is easy to talk about carbs and fats in isolation, but very few foods exclusively have one macronutrient or the other. Food is almost always a packaged deal. When presented with both types of fuel, the body happily will use the carbs first, then the fats. However, in the case of caloric needs being met with carbs, the body will store the fat to save in case of food deficits. “Burn the carbs, store the fats” is the general principle the body uses because this results in maximum energy conservation.
Claim Analysis: Fat You Eat is the Fat You Wear
“The fat you eat is the fat you wear” is more accurately formulated as, “The fat you eat in combination with carbohydrates that meets your daily caloric needs, is the fat you wear.”
Claim Analysis: Carbs will make you fat
“Carbs will make you fat” is more accurately formulated as, “The more carbs you eat, the more dietary fat is stored as fat in the body.”
Mayo clinic fat recommendations per day: 44 to 78 grams.
The process of converting carbs to fat results in about a 10% energy loss in what is stored, so the body prefers not to do this.
Sources:
J.P. Flatt, Conversion of Carbohydrate to Fat: http://www.jlr.org/content/11/2/131.full.pdf