Why does expenditure decrease with weight loss?
To better understand metabolic adaptation, it’s useful to consider the the impact of weight loss on the four components of energy expenditure.
Basal Metabolic Rate
There is a small decrease in metabolic rate as weight is lost, as there is less tissue that needs to be maintained.
Even though fat tissue has lower energy requirements for maintenance than muscle, it still requires energy to be maintained.
Thermic Effect Of Food
Weight loss is often associated with a decreased food intake, which reduces the thermic effect of food.
This can sometimes be offset when small calories changes are made and/or when protein intake is increased, which might be the case if exercise is the primary variable for weight loss.
However, TEF tends to decrease while dieting (but fewer calories facilitates an energy deficit).
Non-Exercise And Exercise Activity Thermogenesis
This is a tricky one because we need to be careful when looking at comparisons.
For many people, NEAT and EAT increase from the start of their regime, particularly if transitioning from a low-activity lifestyle to moderate-high activity level.
However, once the exercise is set, this can begin to decline
Let’s say someone is doing four 45-minute workouts once they are six weeks into the regime.
If they are doing the exact same training program, with similar intensity, at the 24-week month mark their EAT has probably decreased.
The decrease in body weight reduces energy requirements for movement, while improved fitness increases the efficiency of energy production.
It’s important to note that these adaptations are often offset, if not exceeded, by an increase in fitness that allows the individual to increase their training volume.
The decrease would only be noted for the same activity and intensity, from week one to week 24.