TITULO weight loss
⚖️ Weight Loss
The most complete guide to weight loss science, myths and treatments. Caloric deficit, diets, exercise, medications, surgery and everything you need to know.
⚖️ Can I eat whatever I want with intermittent fasting? Does apple cider vinegar burn belly fat? The truth about weight loss
I'm going to start with a confession that no miracle diet guru will tell you:
No, you cannot eat whatever you want during the 8 hours of intermittent fasting. No, apple cider vinegar does not burn belly fat. No, lipolysis injections do not dissolve fat while you eat whatever you want. And no, you won't become Iron Man by losing weight.
1️⃣ Caloric deficit → It's the only mechanism to lose fat. Without deficit, there is no loss.
2️⃣ Consistency > Perfection → It's not about miracle diets, but sustainable habits.
3️⃣ Obesity is a chronic disease → With genetic, metabolic and environmental components.
4️⃣ There are tools that help → Medications (Ozempic, Wegovy, Mounjaro) and bariatric surgery, but they are not magic shortcuts.
🔍 Use the table of contents to navigate over 100 questions about science, myths, diets, exercise, medications, surgery and psychological aspects.
📑 Table of Contents
Reducing total body mass, which includes fat, muscle, water and other tissues. The healthy goal is to lose fat, not just weight.
Losing weight: the scale goes down, but it could be due to water loss, muscle loss or even bone mass. Losing fat: you reduce adipose tissue, which improves health and body composition.
0.5-1 kg (1-2 lbs) per week is a healthy and sustainable rate. Losing faster usually involves muscle loss, dehydration and rebound effect.
It's when you consume fewer calories than you burn. It's the only mechanism to lose fat. Without a caloric deficit, there is no weight loss, regardless of what you eat.
Approximately, yes. The caloric deficit is mainly achieved through diet (it's easier not to eat 500 calories than to burn them at the gym). Exercise is essential for health, muscle maintenance and preventing rebound, but it's not the main tool for weight loss.
BMI is a screening tool, not a diagnosis. A bodybuilder with high muscle mass can have a BMI >30 and not be obese. Obesity is clinically defined as BMI ≥30 kg/m² (≥27.5 in South Asian or African descent populations). Waist circumference is also important: >80 cm in women or >94 cm in men indicates higher metabolic risk.
Because your body is designed to defend its weight. When you lose weight, compensatory mechanisms are activated: increased ghrelin (hunger), slower metabolism, less caloric expenditure when moving, and more cravings for calorie-dense food. It's not lack of willpower. It's biology.
The one you can maintain over time. There is no universal "best diet". Evidence points to: moderate caloric deficit, high in protein (to preserve muscle), high in fibre (for satiety), low in ultra-processed foods, and sustainable for you.
Yes, for short-term weight loss, because it reduces appetite and eliminates water. But it's hard to maintain, can cause side effects (constipation, bad breath, fatigue, increased LDL cholesterol in some people), and is not superior to other diets in the long term.
Intermittent fasting is an eating pattern that alternates between fasting and eating periods. The most common form is 16:8 (16 hours fasting, 8 hours eating). It works because it reduces total caloric intake (by having fewer hours to eat). It has no magical effects beyond caloric deficit.
No. Carbohydrates are an important source of energy and fibre. The problem is the type of carbohydrates we eat. Unrefined carbohydrates (oats, fruits, vegetables, whole grains, potatoes, sweet potatoes) are healthy. Refined carbohydrates (white flour products, sugary drinks, pastries) should be avoided or only consumed occasionally.
Not necessarily. Fats are essential for hormonal health and vitamin absorption. Unsaturated fats (olive oil, oily fish, nuts, avocado) are healthy. The problem is trans fats and excess saturated fats. However, fats have more calories per gram (9 kcal/g) than carbohydrates or proteins (4 kcal/g), so portion control is important.
No. Bread is not bad in itself. The problem is excess and what you put on it (butter, oil, cold cuts). Whole grain or rye bread has more fibre and is more satiating.
Not for weight loss. Skipping breakfast is a form of intermittent fasting. There is no evidence that "breakfast is the most important meal of the day" for weight loss. What matters is the total daily caloric intake, not when you eat.
Most have no solid evidence. The only ones with some (small) effect are caffeine and green tea. Supplements that "work" often contain unregulated ingredients (ephedrine, sibutramine, DNP) that are dangerous. There are no magic pills.
"Light" products have fewer calories than normal ones, but they're not magic. The problem is that people often compensate by eating more. Zero-calorie drinks don't directly make you gain weight, but they're not healthy and may increase sugar cravings in some people.
The ideal is to combine both. Cardio burns more calories during exercise. Weights increase muscle mass, which raises your basal metabolic rate (muscle burns calories at rest). Also, strength training is key to avoiding sagging skin and rebound effect.
Yes. Walking 8,000-12,000 steps per day burns approximately 300-500 extra calories. It's low impact and sustainable for most people.
It burns a higher proportion of fat as fuel, but the total calories burned is usually similar. There is no solid evidence that it's superior for total fat loss.
Yes, with diet alone. But you will lose muscle as well as fat, which slows your metabolism and increases the risk of rebound and sagging. Exercise is highly recommended.
Ozempic is an injectable medication with semaglutide (a GLP-1 agonist). Originally for type 2 diabetes, it is also used for weight loss. Wegovy is the same molecule at a higher dose, specifically approved for the treatment of obesity.
Mounjaro contains tirzepatide, a dual GLP-1/GIP agonist. It is more potent than semaglutide for weight loss, with an average loss of 15-21% of body weight in studies.
Yes, when used under medical supervision. Major obesity societies have stated that these medications are safe, effective and appropriate for long-term use. The most common side effects are gastrointestinal (nausea, vomiting, diarrhoea).
In studies, when the medication is stopped, most people regain the lost weight (rebound effect). That's why it's considered a chronic treatment (like hypertension or diabetes).
Rapid weight loss with semaglutide can include a proportion of muscle mass (20-40% of lost weight). This is prevented with strength training and high protein intake. It's not a direct effect of the drug, but of rapid weight loss.
Not indicated. These medications are for treating obesity as a disease (BMI ≥30 or ≥27 with comorbidities). Using them for cosmetic weight loss is dangerous and has caused serious adverse effects.
Surgical procedures to reduce the size of the stomach and/or alter nutrient absorption. The most common are gastric sleeve (removal of 80% of the stomach) and gastric bypass (restriction + malabsorption).
According to NICE: BMI ≥40, or BMI ≥35 with comorbidities (diabetes, hypertension, sleep apnoea), or BMI ≥30 with recently diagnosed type 2 diabetes.
A study presented at ASMBS 2026 with over 107,000 patients showed that bariatric surgery offers greater long-term protection against heart attacks, strokes and death than GLP-1 drugs in older adults with obesity and diabetes. At 5 years, the risk of major cardiovascular events was almost 16% lower in the surgical group.
It has risks, like any major surgery. Mortality is low (<0.3% in centres of excellence). Its safety profile is comparable to other common surgeries like cholecystectomy or knee replacement.
It's very common. Sagging skin may require body contouring surgery (tummy tuck, arm lift, etc.) if it causes health problems (skin fold infections) or for aesthetic reasons.
Yes, in a percentage of patients. Surgery is a tool, not a magic cure. If the stomach is stretched or bad habits return, weight can be regained.
It's not your fault. Obesity is a chronic, complex, recurrent disease with genetic, epigenetic, metabolic, psychological, social and environmental components. Genetics predispose, but environment and habits determine. The American Medical Association recognised obesity as a disease back in 2013.
On average, yes. Women naturally have a higher body fat percentage (for reproductive reasons), a lower basal metabolic rate, and hormonal fluctuations (menstrual cycle, menopause) that can make weight loss more difficult.
Hypothyroidism slows metabolism and can cause weight gain. With proper treatment (levothyroxine), metabolism normalises and you can lose weight with the same principles as anyone else.
Yes. Lack of sleep increases ghrelin (hunger), reduces leptin (satiety), increases cortisol (stress) and reduces energy to exercise. Sleeping less than 7 hours is associated with higher BMI.
Yes. Elevated cortisol increases appetite (especially for high-calorie, sugary foods), promotes abdominal fat accumulation (the most dangerous for health) and reduces motivation to exercise.
It's the desire to eat not due to physiological need, but due to emotions (boredom, sadness, anxiety, stress, happiness). It's an emotional regulation mechanism. Identifying it is the first step to managing it.
- Protein and fibre at every meal (satiety)
- Eat slowly (satiety takes 20 minutes)
- Drink water before meals
- Avoid sugars and ultra-processed foods (they trigger hunger)
- Sleep well (lack of sleep increases ghrelin)
It's regaining lost weight (and often more) when returning to previous habits. It happens because very restrictive diets slow metabolism and cause muscle loss. When returning to normal eating, weight is regained faster.
It depends. If you eat 3000 extra calories, yes. If you eat one more calorie-dense meal (800-1000 extra calories), you can compensate. Cheat meals can help with psychological adherence, but they don't speed up metabolism.
No. Extreme cold (like in medical cryolipolysis) can damage adipocytes, but with controlled medical equipment. An ice cube does nothing.
Technically yes: your mass is the same, but your weight (the force of gravity) is less. On the moon, you would weigh 1/6 of what you weigh on Earth. But your body mass (the amount of matter) doesn't change.
Tears are water. If you cry a lot, you temporarily lose water. It's not fat loss.
0.5-1 kg (1-2 lbs) per week is a healthy and sustainable rate. Faster loss usually involves muscle loss, dehydration and rebound effect.
Consuming fewer calories than you burn. It's the only mechanism to lose fat.
Yes, because it helps reduce total caloric intake. It has no magical effects beyond caloric deficit.
No. Excess calories make you gain weight, not timing.
No. A study claiming this was retracted due to physiologically impossible results.
A medication with semaglutide for type 2 diabetes and obesity. It produces 15% weight loss in one year under medical supervision.
It has risks like any major surgery, but mortality is low (<0.3% in centres of excellence).
Yes, but you'll lose muscle and have a higher risk of rebound and sagging. Exercise is highly recommended.
Most don't. The ones that "work" do so marginally and some are dangerous.
No. Obesity is a chronic disease with genetic, metabolic and environmental components.
Yes, unfortunately. Weight bias in job interviews, promotions and salaries is well documented. It's a form of discrimination with real consequences.
Yes, of course. Happiness doesn't depend on weight. There are thin unhappy people and obese very happy people. Health and self-esteem are more complex than a number on the scale.
To a large extent, yes. The diet industry makes money when you fail (because you buy the next product). Many fad diets have no scientific basis and are designed to be unsustainable.