When people eat fewer calories, their cognitive performance may change due to shifts in resting metabolic rate, not because of changes in their weight or body fat. The key factor appears to be how the body regulates energy use at rest.

In people who are not overweight, eating fewer calories does not lead to better thinking skills by changing how much energy they use in a day or how active they are, because those changes are not linked to thinking ability once their resting metabolism is taken into account.

In healthy adults between 21 and 50 years old, reducing calorie intake by 25% for two years is linked to modest improvements in memory and metabolic rate, even when body weight and total energy consumption do not change, which may indicate that changes in how the body uses energy influence cognitive function.

In healthy adults who reduce their calorie intake over a long period, changes in the rate at which the body uses energy at rest are linked to changes in cognitive performance, even when total calorie burn and physical activity levels are accounted for.

In adults who are not obese, a higher resting metabolic rate is linked to better cognitive performance at rest, even when accounting for body size and how much energy they consume.