This article is part of our series of objective nutritional analyses, contrasting the biological evidence with popular promises.
Few nutritional trends have sparked as many passionate debates, bestselling books, and social media posts over the past decade as the ketogenic diet, or keto. Once an almost century-old clinical treatment for children with refractory epilepsy, it has come to be hailed as the ultimate formula for burning fat, sharpening mental focus, and reprogramming our metabolism.
But behind the unbridled enthusiasm and the butter-coffee recipes, it is worth separating proven physiology from marketing promises. What really happens in your body when you almost entirely eliminate carbohydrates? Is it sustainable and healthy in the long run?
1. What does nutritional ketosis really involve?
The human body normally uses two main types of fuel: glucose (derived from the carbohydrates we eat and from the glycogen stored in the liver and muscles) and fatty acids. On a conventional diet, glucose is the preferred energy source for most tissues, especially the brain.
The keto diet proposes a radical shift in the distribution of macronutrients:
- Fats: 70% to 80% of total daily calories (extra virgin olive oil, avocados, nuts, oily fish, eggs, and meats).
- Proteins: 15% to 20% (moderate, to prevent excess amino acids from being converted into glucose through gluconeogenesis).
- Carbohydrates: 5% to 10% (generally a strict limit of fewer than 20 to 50 grams of net carbohydrates per day).
Once the liver’s glycogen stores are depleted after several days of restriction, the liver begins to oxidize fat massively and to produce ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone). These molecules cross the blood-brain barrier and act as a highly efficient alternative fuel for the central nervous system.
2. Why it’s taking over: The proven benefits
The popularity of the keto diet is no accident; when implemented correctly, it produces very noticeable physiological effects:
- Rapid initial loss of volume and weight: By depleting liver and muscle glycogen (each gram of glycogen holds between 3 and 4 grams of water), a rapid elimination of fluids occurs in the first week. Although it is not all fat, the motivational impact on the scale is immediate.
- Powerful appetite control: This is its greatest practical advantage. Ketone bodies have a direct satiating effect and reduce the secretion of ghrelin (the hormone that stimulates hunger). The sharp drops in blood sugar and the pressing need to snack between meals come to an end.
- Improvement of metabolic markers in type 2 diabetes: By removing the carbohydrate substrate, blood glucose spikes practically disappear and baseline insulin levels drop drastically, improving insulin sensitivity and lowering triglycerides.
«Ketosis is not a mystical state of metabolic enlightenment, but rather an evolutionary survival mechanism that allowed us to make it through long periods of scarce fruit and vegetation.»
3. The other side of the coin: Drawbacks, risks, and social life
Despite its clinical virtues, maintaining a ketogenic diet in the modern world comes with serious trade-offs that are often downplayed:
- The “keto flu”: During the first or second week of adaptation, the accelerated loss of water carries away sodium, potassium, and magnesium. Common symptoms include headache, muscle weakness, dizziness, irritability, and nausea. It requires consciously replenishing salts with electrolytes or MCT oil powder (Myprotein code DAVID-R495F) and verifying ketosis with ketone test strips on Amazon.
- Low fiber intake and microbiota dysbiosis: By eliminating legumes, whole grains, most fruits, and tubers, the intake of prebiotic fiber plummets. Several studies have observed a drastic reduction in beneficial butyrate-producing bacteria (an essential protector of the intestinal lining).
- Impact on the lipid profile (ApoB and LDL): In a significant subgroup of people (“hyper-responders”), a keto diet loaded with saturated fats dangerously raises LDL cholesterol and ApoB, increasing the atherogenic risk.
- Social friction and rigidity: A dinner with friends, a vacation, or a family event turns into a minefield. Falling out of ketosis after eating a serving of sweet fruit or rice takes several days to return to the initial state.
4. Comparison table: The best and worst of the Keto Diet
| Aspect | Rating | Key comments |
|---|---|---|
| Fat loss | ⭐⭐⭐⭐ High | Effective in the short and medium term thanks to high satiety. |
| Mental clarity | ⭐⭐⭐⭐ Notable | Glycemic stability with no postprandial fog. |
| Sustainability | ⭐⭐ Low | Very difficult to sustain for years in real life. |
| Gut health | ⭐⭐ Fair | Lack of prebiotic fiber diversity. |
| Anaerobic performance | ⭐⭐ Fair | Explosive maximal-strength sports may suffer. |
The Trebellos verdict
The ketogenic diet is a very powerful therapeutic tool for specific situations: severe insulin resistance, certain neurological conditions, or brief nutritional reset protocols. However, turning it into a perpetual lifestyle rarely makes up for the loss of life flexibility and the sacrifice of foods as healthy and rich in polyphenols as legumes, apples, or seasonal berries. Metabolic flexibility consists of knowing how to burn fat and carbohydrates with ease, not being trapped forever in only one of the two fuel stores.
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