Sugary drinks before and during pregnancy raise the risk of gestational diabetes by 22%. Diet in pregnancy and infancy may set up obesity for life, so this is one group where getting weight gain right matters most.

Calories in versus calories out is true, but insulin controls what happens next. High blood sugar stores fat and low blood sugar releases it. This chapter shows why low-carb diets beat calorie restriction and how the conflicting advice fits together.

Leptin diets follow five simple rules, but the leptin explanation has no scientific basis. They work because they cut sugar and carbohydrate, raise protein and limit calories. Believe it if it helps, but skip the extra supplements.

There is no science showing your blood type decides what you should eat, and the lectin theory fails. Yet the diet works for many people because it removes processed food and wheat. Wrong theory, useful result.

Atkins roughly doubled the weight loss of rival diets in a Stanford trial. It works because protein fills you up and sugar and simple carbohydrates drop out, not because of ketosis. It targets weight more than health, and the pre-packaged products cost.

The Paleo diet removes sugar, grains and processed food, and people lose weight without counting calories. The author likes the results but doubts the cave-man story, since we do not really know what our ancestors ate.

Reality shows like The Biggest Loser teach viewers that weight is only willpower. Research finds they raise anti-fat attitudes, and stigma makes people less likely to lose weight and keep it off. The clear winners are sponsors and the diet industry.

When coconut-and-fish communities adopt sugar and flour, diabetes, gout and obesity follow. Studies of Tokelau islanders and the Inuit point to refined carbohydrates as a main cause, though sugar and flour are hard to separate.

Of more than 660 diets, few have a good long-term record. Only one in ten dieters is still dieting after a year. This chapter shows why calorie restriction fails, what diet trials really found, and why surgery is no easy fix.

BMI is a rough guide, not a verdict. Weight mixes bone, muscle and two kinds of fat, and belly fat is the most harmful. Measure your waist: if it is less than half your height, your weight risk is probably low.