What are metabolism and weight changes?
All humans take in energy (in the form of food) and then burn that energy as the fuel to keep all life functions, like breathing and brain activity, happening. Metabolism can be defined as the conversion of food into chemical energy that is used to power the body’s activities and to build all parts of the body’s structure, including bones, muscle and fat.
Changes in weight, whether increasing or decreasing, can be simplistically viewed as energy imbalances happening between energy in and energy out. This energy in and out is called total energy expenditure.
The term ‘total energy expenditure’ is made up of three interacting components:
- the base rate at which your body burns calories to stay alive and functioning properly (your metabolic rate);
- the energy used to break down food (dietary thermogenesis); and
- physical activity (which determines how much energy is used during physical activities of daily living like moving around, breathing and exercising).
In sedentary adults (those who are generally inactive), base or resting metabolic rates account for about 60% to 70% of total energy output, the dietary thermogenesis for around 10%, and physical activity for the remaining 20% to 30%. These proportions change if physical activity is increased, depending on the amount and intensity of the activity. As more energy is used due to increased physical activity, the rate at which your base metabolism burns energy increases. So, with movement and physical activity, not only does the amount of energy burned increase directly as a result of the activity, but it also increases the rate at which your body burns energy while resting.
Energy from food is stored in the form of adipose tissue (fat) beneath the skin (called subcutaneous fat) and around the organs (called visceral fat or central adiposity). This is normal and healthy, and because central adiposity is not the same as subcutaneous belly fat, even those who may be considered normal or underweight may still be impacted by central adiposity. Central adiposity can increase as a result of a sedentary lifestyle, a decrease in healthy recreational movement and exercise, decreased quality of sleep, shift work, and a poor diet.
However, changes to the proportions of central adipose tissue versus subcutaneous adipose tissue can lead to obesity and to other serious health concerns such as metabolic syndrome. This syndrome is a cluster of conditions such as high blood pressure and abnormal cholesterol levels that increase the risk of heart disease, stroke and type 2 diabetes.   
Women in the menopausal transition typically gain weight and experience changes in the composition of their body fat . The increase in body mass index (BMI – one commonly used measure of adiposity), is seen in multiple studies regardless of menopausal status, so menopausal changes are not the only cause. However, the increased storage of central adipose tissue is clearly linked to menopausal stage. 
Subcutaneous body fat is positively associated with vasomotor symptoms (primarily hot flashes), so the more body fat you have, the more likely you are to have vasomotor symptoms. This is consistent with the model of body fat acting as an insulator. The relationship between fat gain and hot flashes is most pronounced among Caucasian and Chinese women, compared to African-American or Japanese women. However, no consistent associations between subcutaneous fat gain and night sweats was observed in the study.