The keto diet can be an effective short‑term method for supporting weight loss. However, its long‑term effects remain unclear, and due to its highly restrictive nature, it may lead to yo‑yo dieting once discontinued.
When following a keto diet, it is important to pay attention to the type and quality of fats.
The keto diet is not suitable for everyone, and in certain conditions, it is essential to discuss its inclusion with a doctor.
What is keto diet?
The keto diet is characterised by a significant restriction or complete elimination of carbohydrates from the diet. As a result, fats make up the largest portion of daily intake, followed by proteins. Although there is no official definition that regulates the exact ratio of macronutrients, the following proportions are most commonly used in practice, based on total energy intake (TEI):
Fats: 55–60% of TEI
Proteins: 30–35% of TEI
Carbohydrates: 5–10% of TEI
Where did keto diet come from?
The keto diet was originally used as a therapy for epilepsy in children, where Dr. Wilder, in 1921, noticed that this dietary adjustment led to a reduction in the number and intensity of seizures. At that time, the ketogenic diet was the main method for treating epilepsy. Its importance diminished with the advent of modern medications—antiepileptics. Even today, however, the diet remains a valuable option for patients whose seizures do not respond to conventional treatment. That said, it is not suitable for everyone. For each patient, medical professionals must carefully evaluate various internal and external factors before deciding whether a ketogenic diet is appropriate as part of treatment.
Keto diet and weight loss
In recent years, the keto diet has gained widespread popularity as a weight‑loss strategy, featured in television adverts, billboards, and countless online promotions. It’s easy to get the impression that the fewer carbohydrates you eat, the slimmer and healthier you’ll become. But is that really the case?
How does keto diet work?
Carbohydrates are the body’s main source of energy. Compared with fats and proteins, they are digested more quickly, and in the case of simple sugars, the body can access energy almost immediately, which is a process often relied upon by endurance athletes.In a balanced diet, carbohydrates typically make up the majority of daily energy intake, around 45–60%. After consuming carbohydrates, blood glucose levels rise, which activates the release of the hormone insulin, which "stores" glucose in cells, where it serves as an energy source.
Glucose is therefore essential to human metabolism. If the body doesn’t receive enough from food, it begins to produce it through other means or shifts to alternative energy sources. This is exactly what happens on the keto diet. With significant carbohydrate restriction, the body mainly uses the processes of gluconeogenesis and ketogenesis.
During gluconeogenesis, the body produces glucose from other substrates, such as amino acids, pyruvate, lactate or glycerol, which is produced by the oxidation of fats. Some tissues, such as red blood cells, parts of the brain and the liver, can only use glucose for energy. However, gluconeogenesis alone cannot meet the energy demands of all tissues efficiently. As a result, the body turns to an alternative energy source: ketone bodies. These include acetoacetate, beta‑hydroxybutyrate and acetone. When the body increases the production and use of these molecules as fuel, the state is referred to as nutritional ketosis.
Does keto diet always lead to weight loss?
You may recall that the production of ketone bodies involves fat oxidation, often interpreted as “fat burning.” This raises a natural question: does the keto diet automatically lead to weight loss? In reality, this is not the case; although fats are indeed used for this purpose, the primary variable for weight loss remains energy balance. If you achieve a caloric deficit on the keto diet, you will lose weight, just as you would on any other diet with 45–60% carbohydrates. If you do not achieve a caloric deficit, you simply will not lose weight.
Upon closer inspection, you will find that the keto diet essentially significantly restricts the intake of one macronutrient, which in some cases may lead to a caloric deficit, because, for example, bread or side dishes that you would otherwise eat, you suddenly cannot have. However, if you compensate for the missing foods by putting a larger portion of fat or protein on your plate, there will be no change, and you will simply deprive your diet of carbohydrates, along with many other substances and micronutrients of which they are a natural source.
Scientific studies and weight loss on keto diet
Some studies confirm the short‑term effectiveness of the ketogenic diet for weight reduction. Contributing factors may include the fact that meals rich in fats and proteins tend to be more satiating, helping to reduce feelings of hunger. Research has also shown that the keto diet can influence hormones regulating satiety, further lowering the desire to eat. Another potential effect is attributed to the increased energy demands on the body, which result from the need for gluconeogenesis.
However, a key limitation is that most studies on keto and weight loss have been conducted over short‑term periods. Evidence on the long‑term effects remains limited. This raises questions about whether the results achieved are sustainable or whether returning to a balanced diet leads to weight regain, known as the yo‑yo effect. Studies focusing on keto diets often report a high dropout rate, highlighting how challenging it can be for the general population to adhere to its strict principles in the long run.
Possible risks of keto diet
Like any restrictive eating pattern, the keto diet carries potential disadvantages and health risks, particularly when followed without medical supervision or professional guidance. One of the main concerns is insufficient energy intake or micronutrient deficiencies. Foods rich in carbohydrates are a natural source of many substances that you are suddenly forced to eliminate from your diet.
Especially powdered keto diets focused on weight loss may not take into account the individual needs of a given person, and there is a real risk of too low energy intake, which can then lead to health complications. Another factor is maintaining weight after "discontinuing" the keto diet—even if it was effective over several weeks, its principles did not teach you anything about how to eat in the long term. If you return to your old eating habits, your weight will likely increase again.
A diet high in fats and low in fibre can lead to digestive problems such as diarrhoea, constipation or cramps. Over time, as the body adapts to the new eating style, these symptoms should subside. Alternatively, fibre can be supplemented with psyllium, etc. It is also important to pay attention to the selection of fats, as they are present in really high amounts in the keto diet. For this reason, it is essential to choose mainly unsaturated fatty acids. Excessive consumption of saturated fatty acids, or even trans fatty acids, could lead to an increased risk of heart and vascular diseases.
How long should you stay on keto diet?
Given the above information, this is a particularly challenging question, which is also being explored by scientists studying the keto diet. Although the keto diet, when properly implemented, appears to be an effective way to reduce weight in the short term (e.g., as recommended by a doctor for individuals with a high degree of obesity), the long‑term effects of the keto diet on the body are not fully understood. In the literature, the duration of the keto diet ranges from 3 weeks to about 6–12 months.
In this respect, it will therefore depend mainly on your goals and needs—even before starting the keto diet, it is advisable to realise that permanent weight reduction can only be achieved when you make long‑term changes to your current lifestyle, even if you lose weight after several weeks on the keto diet, after returning "to your old ways," your weight will likely return to where it was, and possibly even higher due to the yo‑yo effect.
If you suffer from any illness, especially kidney, heart and vascular, liver, neurological diseases or diabetes associated with the use of antidiabetics or insulin, always consult your doctor before starting the keto diet.
Keto diet example meal plan
Adapting to a ketogenic diet typically takes several days, and during this transition period, you may experience temporary symptoms such as irritability or fatigue. However, after a few days, these symptoms should subside. Below is an example of a keto meal plan:
- Energy: 2,571 kcal (10,800 kJ),
- Carbohydrates: 40g (160 kcal / 680 kJ),
- Proteins: 117g (468 kcal / 1,989 kJ)
- Fats: 213g (1,917 kcal / 8,094 kJ),
- Fibre: 18g
- Breakfast: 2 eggs, sautéed green beans (50g) and baby spinach (50g) in rapeseed oil (30 ml), cherry tomatoes (100g)
- Snack I: 2 walnuts (20g) and cucumber (200g)
- Lunch: Roast beef round (100g), rapeseed oil (20 ml), blue cheese (30g), avocado (100g), baby spinach (80g), onion (20g), iceberg lettuce (50g), cherry tomatoes (50g)
- Snack II: 1 hard‑boiled egg, feta cheese (25g), 1/2 pack cottage cheese (75g), cheddar (75g), extra virgin olive oil (10 ml)
- Dinner: Roast salmon with skin (130g), extra virgin olive oil (30 ml), iceberg lettuce (50g), cherry tomatoes (40g), onion (20g), feta cheese (25g)
Bottom line
The keto diet has become very popular in recent years, particularly as a weight‑loss strategy. However, it’s important to remember that the key determinant of weight loss remains a calorie deficit. Although the keto diet can help induce a caloric deficit and reduce feelings of hunger, it is not a miraculous weight loss method.
Plus, commercial powdered keto products carry a real risk of inadequate energy intake and nutrient deficiencies. Another issue is sustainability. Most people can maintain such an “artificial” or highly restrictive diet for only a few weeks, during which they learn very little about balanced nutrition. Consequently, once the diet ends and normal eating resumes, it’s highly likely that lost weight will be regained.
