Neither sugar nor starch are essential nutrients: the body makes its own

Neither sugar nor starch are essential nutrients: the body makes its own

A human being can live without eating a single gram of carbohydrates. This is not gym-bro folklore: the liver and kidneys synthesize the glucose the brain needs through gluconeogenesis, from lactate, glycerol from fats, and amino acids from proteins, and when carbohydrate intake drops sharply, the liver converts fat into ketone bodies that the brain uses as an alternative fuel. The conclusion drawn from the available evidence is uncomfortable for the classic food pyramid: the theoretical minimum intake of carbohydrates as an essential nutrient is zero. Whether it is advisable is another matter.

Which macronutrients are indispensable and which are not

Fats truly are non-negotiable. The body lacks the Δ12 and Δ15 desaturase enzymes, so it cannot produce linoleic acid (omega-6) or alpha-linolenic acid (omega-3): they can only be obtained through food. Without fat, the fat-soluble vitamins A, D, E and K cannot be absorbed, and the cell membranes of every tissue are made of lipids. The minimums to avoid deficiency are around 2.5% of total energy from omega-6 (about 10 g/day) and 0.5% from omega-3 (about 2 g/day). The EFSA and the WHO place total fat intake between 20% and 35% of daily calories, with at least two thirds in mono- and polyunsaturated form.

The historical evidence is not theoretical. In 1938, Burr and Hansen fed a healthy man a virtually fat-free diet for six months and watched his serum linoleic acid fall by 40%, comparable to experimental deficiency in rats. In parenteral nutrition, essential fatty acid deficiency appears between ten days and four weeks without lipid intake, with dermatitis, hair loss and greater susceptibility to infections. There is one documented case of a patient who died after seven months with profound omega-6 and omega-3 deficiency.

Why fiber is not as dispensable as it seems

Here the nuance matters. Complex carbohydrates are the main source of dietary fiber, and fiber sustains the gut microbiome. The recurring joke —living without fiber and ending up with a wrecked gut— has a real basis, although the more precise answer is that FODMAPs are the very first thing removed when gut problems arise, which shows that the relationship between fiber and digestive health is far from linear. The rest of the package matters too: whole grains, legumes and vegetables provide vitamins, minerals and phytonutrients that are hard to get from protein and fat alone.

What the studies say about eating very few carbs

Surviving is possible; living better is another discussion. Studies published in The Lancet and in the Asia Pacific Journal of Clinical Nutrition associate very low carbohydrate intake —less than 40% of calories— with higher mortality and greater cardiovascular and cancer risk. The range the scientific community considers optimal sits between 50% and 55% of daily calories, prioritizing complex, whole-food sources. The WHO confirms that sugar is not an essential nutrient and recommends that free sugars not exceed 10% of total calories.

The mistake of lumping ice cream and lentils together

The strongest criticism of the anti-carb narrative is not nutritional, it is logical. The glucose and fructose molecules are identical whether they come from lentils, a pear, an ice cream or a soft drink: what changes is the food matrix, the fiber that accompanies them, the estimulante ilegal of absorption and everything else. Equating refined sugar with legumes is simplifying to the point of absurdity. And there is a detail that is often forgotten: sore muscles have nothing to do with carbohydrates, they are micro-tears from unaccustomed exercise, especially during the eccentric phase. What you do notice without carbs is reduced performance in intense efforts, because muscle glycogen is the fast fuel for sprints.

The human body has been adapting to scarcity for thousands of years, and that metabolic plasticity is real. But adapting by sacrificing some parts to maintain others comes at a cost, and some things do not come back. With carbohydrate consumption at the center of public debate, the reasonable prediction is that the discussion will shift from "can it be done" to "at what price", although nobody yet knows exactly how long the bill takes to arrive.