Nutrition for Weight Loss: What the Evidence Actually Says

The internet is full of conflicting nutrition advice. Low carb versus low fat. Intermittent fasting versus calorie counting. Keto versus Mediterranean. The good news is that the evidence points to some clear principles that apply regardless of which specific dietary approach you take.

The most important principle: a sustainable calorie deficit

Weight loss requires a calorie deficit — consuming fewer calories than the body expends. But the size and sustainability of that deficit matters enormously. A deficit of 500 calories per day produces roughly 0.5 kg of weight loss per week and is generally sustainable. A deficit of 1,000 calories or more per day may produce faster initial results but is harder to maintain and more likely to cause muscle loss.

Protein: the most important macronutrient for weight loss

Protein is the most satiating macronutrient — it keeps you feeling full for longer than carbohydrates or fat. It also has a higher thermic effect, meaning the body burns more calories digesting it. And it helps preserve muscle mass during weight loss, keeping metabolic rate higher. Good sources include lean meat, fish, eggs, dairy, legumes, and tofu. Aim for 1.2–1.6 g of protein per kilogram of body weight per day.

Fibre: your best ally

Fibre slows digestion, promotes satiety, feeds beneficial gut bacteria, and helps regulate blood sugar. Most UK adults consume far less than the recommended 30 g per day. Vegetables, fruit, wholegrains, legumes, and nuts are all excellent sources.

Ultra-processed foods

Research consistently shows that diets high in ultra-processed foods are associated with higher calorie intake and weight gain — independent of their calorie content. They are engineered to override satiety signals and are typically low in protein and fibre. Reducing them, rather than eliminating them entirely, is a realistic and effective goal.

Practical principles

• Fill half your plate with vegetables at most meals
• Include a source of protein at every meal
• Choose wholegrains over refined grains where possible
• Drink water as your main beverage
• Eat slowly and without screens

For personalised nutrition advice as part of a doctor-led programme, speak to the Weight Loss Wales team.