Why are fats beneficial in a low-carbohydrate diet and harmful in a high-carbohydrate diet?

The ratio of proteins and fats 1:2 in a low-carbohydrate diet. When a person follows a low-carbohydrate diet (for example, keto), the main source of energy shifts from glucose to fatty acids and ketone bodies. In this state:

• Carbohydrates are virtually absent, insulin levels decrease;
• The body actively breaks down fats (lipolysis) for energy;
• The liver produces ketones from fats, which replace glucose for the brain, muscles, and other tissues.

In such conditions, fats become fuel, while proteins serve as building material and a backup energy substance (through gluconeogenesis). A ratio of 1:2 (proteins:fats) is considered physiologically justified:

• Excess proteins will be converted into glucose, which will interfere with ketosis;
• Fats should be more abundant to ensure sufficient ATP levels, especially from saturated fatty acids;
• At the same time, protein intake should not be less than normal to prevent the breakdown of one's own muscles and immune proteins.

Why such a ratio leads to atherosclerosis and obesity on a high-carbohydrate diet. When the diet is high in carbohydrates, with simultaneous high intake of fats (especially saturated), metabolism reacts quite differently:

1. Insulin is high – carbohydrates raise blood glucose levels, to which the body responds by releasing insulin. Insulin: blocks fat breakdown (inhibits lipolysis), promotes fat synthesis (lipogenesis), stimulates fat accumulation in tissues.
2. Fat is not burned – it accumulates, as the body prefers to burn glucose first.
3. Atherogenic lipoproteins are formed – especially in conditions of excess glucose and insulin. VLDL (very low-density lipoproteins) and LDL (low-density lipoproteins) are synthesized more actively. These particles are more easily oxidized and damage the endothelial cells of blood vessels. The formation of atherosclerotic plaques begins.
4. Obesity – especially visceral, increases, as fat is easily deposited with an excess of energy coming from carbohydrates and fats simultaneously.

Biochemical essence. In a low-carbohydrate diet: fats = fuel, proteins = structure + a little glucose (through gluconeogenesis). In a high-carbohydrate diet: glucose = main fuel, while fats are "excess," if not burned, they accumulate.

Therefore, the ratio of proteins and fats should be adapted to the proportion of carbohydrates in the diet.

• A low-carbohydrate diet requires more fats, fewer proteins (within normal limits), and almost zero carbohydrates.
• A high-carbohydrate diet requires limiting fats (especially saturated) to avoid metabolic conflict and fat accumulation.