January arrives full of new resolutions: taking better care of yourself, exercising more, eating “healthier”… and for many people, losing weight. After the holidays, social media fills up with challenges, miracle diets and promises of quick changes. Everything seems to revolve around “getting back on track” and “compensating for excess.”
But here’s the important question: at what cost? The pressure to lose weight quickly leads many people to follow extreme diets without realizing they may be damaging their metabolism, digestion and relationship with food.
That’s why, as a registered dietitian specialized in weight loss and eating behavior disorders, today I want to talk to you honestly and with scientific evidence about when weight-loss diets can become dangerous and what healthier alternatives really look like — without punishment or extremes.
Types of dangerous diets
A. Mono-diets
Mono-diets are based on eating almost only one food or food group for several days, such as “the pineapple diet,” “the artichoke diet,” “the apple diet,” “the egg diet,” and countless other miracle diets.
Although there may be a rapid initial drop in body weight, this loss is mainly due to the loss of fluids and muscle mass, not body fat. Most of these diets are low in carbohydrates, which means that our glucose stores in the liver and muscles, known as glycogen, are depleted without being replenished. To store glucose in the form of glycogen (not fat), approximately 4 grams of water are required for each gram of glycogen. Therefore, the initial weight loss largely reflects the loss of this associated water rather than true fat loss. If this pattern is maintained and energy intake remains too low, the body also begins to use muscle tissue as a source of energy. Because muscle weighs more than fat, this is reflected on the scale as a significant weight loss in a short period of time, despite being metabolically harmful.
Main risks:
Vitamin and mineral deficiencies
Lack of protein and healthy fats
Extreme fatigue, dizziness, weakness
Digestive disturbances
Very frequent rebound effect
They also don’t teach you how to eat or build healthy habits. Once the diet ends, weight is usually regained quickly.
B. Very low-calorie diets
Although these diets may include a wider variety of fruits, vegetables, and protein sources, the reality is that diets providing fewer than 1,500 kcal do not meet our micronutrient needs. Over the long term, beyond four weeks, nutritional deficiencies can disrupt our hormones, alter the gut microbiota, and negatively affect metabolism, fertility, and digestion.
Very low-calorie diets are often easy to recognize because intense hunger between meals appears within the first few days. This is the body’s way of signaling that this approach is not appropriate. However, if food intake remains insufficient, the body interprets this as a prolonged situation and switches into survival mode, slowing down metabolism to conserve energy. The result is rapid initial weight loss followed by a plateau.
Additionally, this lack of energy increases cortisol levels—the stress hormone—which, when chronically elevated, can disrupt progesterone secretion and negatively alter the gut microbiota. This has direct adverse effects on fertility, inflammation, immune function, and weight regulation.
C. Detox diets
These diets are typically promoted as a way to “cleanse and detoxify the body” through green juices and plant-based eating aimed at enhancing liver detoxification. They are usually very low in calories and protein.
They often seem appealing or even necessary after holidays, celebrations, weddings, or periods of overeating. In reality, however, what the body truly needs is simply a return to normality: balanced, healthy eating and time to self-regulate. No detox diet is required to restore well-being.
While including vegetables and green juices can indeed support health—thanks to their content of key nutrients that aid liver function—they cannot replace other essential food groups. Vegetables should not displace healthy fats, proteins, or complex carbohydrates (such as whole grains and legumes), as doing so once again puts nutritional balance and overall health at risk.
D. Fasting or skipping meals to “compensate”
Many people choose to skip meals after having eaten “too much” the previous day. However, this pattern can easily lead to a vicious cycle: restriction → intense hunger → binge eating → guilt → restriction.
Associated problems include:
Dysregulation of hunger and satiety.
Increased obsession with food.
Metabolic stress.
Digestive disturbances
Greater difficulty losing weight in the long term.
Rather than listening to the body, this approach becomes a form of punishment. It is strongly discouraged, especially for individuals with a history of eating disorders or an unhealthy relationship with food.
What do these diets have in common?
They are not sustainable over time.
They do not teach how to eat well.
They create fear around certain foods.
They generate guilt.
They increase food obsession.
They prioritize weight over health.
When the diet ends, the problem returns—and many people remain trapped in a “diet after diet” cycle for years.
How should we understand nutrition?
Eating should not be a constant struggle, nor should it be based on:
restrictions extreme control rigid rules numbers on the scale
Instead, it should be:
A lifestyle Flexible Personalized Supportive of digestion, Metabolism, Hormonal balance, And emotional well-being
Nutrition and body weight are not just about calories. Stress, sleep, movement, emotions, and gut health also play a crucial role. Everything is connected. Restricting foods, following overly rigid meal plans, and counting calories can lead to food anxiety, frustration, emotional distress, and a poor relationship with both food and the body.
If you want to lose weight in a healthy, sustainable way, feel free to reach out for nutritional guidance and book an appointment with me.
English 
Spanish 
French