Weight management is fundamentally an energy-balance problem: eating more calories than you burn causes weight gain, eating fewer causes weight loss — but HOW that deficit is created matters for whether it is healthy and sustainable.
The textbook's own target: aim to lose 1-2 kg a week at most (losing weight too fast leaves one feeling sluggish, drained and sick), achieved through a negative energy balance of 500-1000 kcal a day, which translates to an ideal weight-loss rate of 500 g to 1 kg per week. Caloric restriction should always be combined with moderate exercise — aerobic exercise is particularly useful for long-term weight maintenance because it preserves lean body mass and partly prevents the drop in basal metabolic rate that pure calorie-cutting causes.
The 15-point modification list the textbook gives for actually changing what you eat includes: eating from all food groups (never cutting one out entirely); choosing high-fibre foods (fruits, vegetables, beans, whole grains) since they are filling and hard to overeat; nuts in moderation; switching to fat-free/low-fat milk; baking/grilling instead of frying; limiting high-sugar foods (jams, jellies, sweetened curd); cutting high-cholesterol/saturated-fat snacks (mixtures, mathris, namkeens) in favour of high-fibre biscuits or khakhra; choosing low-fat proteins (egg whites, fish, lean meats, poultry); serving smaller portions (using smaller plates/bowls/spoons); cooking at home (restaurant/packaged food has more sodium, sugar, fat and bigger portions); avoiding high-salt foods (pickles, papad — they cause water retention); avoiding high-calorie snacks and convenience foods; cutting soft drinks (one can has 10-12 teaspoons of sugar, ~150 kcal — replace with lemon water, coconut water, lassi or chaach); replacing soda/alcohol/coffee with water (thirst is often mistaken for hunger); and eating frequently (3 small meals + 2-3 snacks) since skipping meals, including breakfast, actually slows metabolism.
The common thread across all 15 points is making smarter food CHOICES rather than simply eating less food overall — which is what makes the approach sustainable instead of a short-lived crash diet.