As a CaseyTrain client you notice weekly changes in calories, cardio, and training. The macronutrient content within the calories in your meal plans are manipulated on a weekly basis. I often get asked why I change certain macros, add or pull cardio, and why cheats or reefed days are implemented. Many factors are considered but one of the biggest ones is Leptin.
Leptin and Body Weight
Leptin boosts metabolism to help regulate body weight. The hormone is secreted from your fat cells, and levels are correlated with body fat percentage. When body fat levels fall, leptin levels decrease and appetite is stimulated; when fat mass rises, the opposite occurs. As you change each week so does your Leptin, this is why macronutrient, cardio, and training manipulation are crucial for sustained progress.
Insulin and Leptin Together
Insulin is a hormone that helps regulate blood sugar. Together with leptin, it regulates food intake and metabolism. When you eat a carbohydrate-containing meal, your blood sugar rises, signaling your pancreas to release insulin. The presence of insulin in the bloodstream triggers pathways in the brain that signal the body to reduce food intake. Insulin and leptin have a combined effect at suppressing appetite, and the two hormones interact in the brain to reduce food intake. This is why macronutrients are manipulated around training.
As with insulin, when levels rise and remain elevated, the body becomes less sensitive to its effects. In response, more leptin is released, leading to leptin resistance. This is why cheats and reefed days are implemented when your body hits a stall.