Our height, structure, predisposition to store fat, and muscularity are genetically determined when we reach puberty. These attributes determine our base shape and appearance, and cannot be changed without surgery or drugs. We can, however, increase or decrease body fat and muscle to sculpt a new shape. Keep in mind, we have a natural limit for muscular potential.

Obesity is primarily caused by behavioural and environmental factorsrather than by genetics, considering there is only a small calorie variance in resting metabolism from person to person.

Your body weight does not consist of just muscle and fat, but also water, blood, organs, waste, tissue, and bones. Your scale tells you your weight, but it doesn’t tell you how much of it is lean muscle and how much of it is fat. If you gain or lose a few pounds over the course of the day, it is likely just fluctuations of water weight. Measuring week-by-week, first thing in the morning, is a more reliable way to track progress.

You can find out your approximate body fat percentage at home with calipers, or at a gym or medical centre that offers DXA scans. You can also roughly guess your body fat percentage by looking at your midsection in the mirror. If you have no visible abdominal muscles, you are likely over 20% body fat (or over 30% for women). If you can see partial outlines of your abs, you are likely 15–19% (25–29% for women). If you can see full abdominal muscles, you are likely at the most 10% (20% for women). Women have higher body fat percentages because of extra adipose tissue in their breasts, thighs, and glutes.

 BMI (body mass index) takes only weight into account, while body fat percentage takes the ratio of muscle mass into account. For that reason, body fat percentage reflects a more accurate picture of overall fitness and health. The DBW calculator below can help you find your desired body weight based on known body fat percentage:

There is little variability with restingmetabolism from person to person, so using labels such as "fast or slow" metabolisms are misleading. Lean mass, the thermogenesis of foods, especiallyprotein, have greater variability on metabolism. The more muscle mass one has, the higher the metabolism. Having three vs. six meals in a day has little effect on metabolism. Metabolism is increased through exercise, especially weight training, due to the energy expenditure during the workout and theenergy required to repair the muscles.

While not a hard rule for illustration purposes, the majority of your body composition (lean mass + fat) is the result from diet. Diet enables you to change your weight. Exercise is a tool to manipulate further change by necessitating the growth of muscle or to accelerate fat loss.

Exercise goes hand-in-hand with nutrition. Exercise provides massivemental and physical health benefits.