Woman Drinking after a Workout

Improving metabolism with diet

Many people blame a ‘slow metabolism’ for their inability to lose weight, or on the other hand those that are able to maintain a healthy weight must have a ‘fast metabolism.’

Metabolism refers to all the chemical processes that allow your body to convert food into energy and allow it to live and function. The amount of energy (calories or kilojoules) your body burns is affected by your metabolism. A more relevant term when we talk about ‘metabolism’ is metabolic rate.

Your body’s metabolic rate is made up of three components.

  • Basal metabolic rate (BMR) – the amount of energy (kJ) you burn at rest and the minimum amount of energy you need to exist. BMR includes the energy the body uses to keep all its systems functioning correctly. This makes up ~50-80% of your body’s total energy use.
  • Energy used during physical activity – dependent on how active you are. In a moderately active person doing 30-45 minutes of moderate activity a day, this will be ~20% of your energy use.
  • Thermic effect of food – The energy needed to eat, digest and metabolise food. Contributes ~5-10% of the body’s energy use.

Basal Metabolic Rate

As the BMR makes up the majority of the body’s total energy use and is influenced mainly by your body composition. Muscle requires more energy to function than fat so those with a high muscle mass will have a higher BMR. This is why men, who generally have more muscle mass than women, have a higher BMR.

BMR is affected by:

  • Height – the taller you are, the larger skin surface for heat loss.
  • Growth – during pregnancy and childhood.
  • Fever and stress.
  • Higher muscle mass.
  • Smoking and caffeine.
  • Environmental temperature – both heat and cold raise BMR.
  • Fasting.
  • Starvation.
  • Sleep.

Strategies to optimise BMR

Make sure you eat enough protein and spread it throughout the day

Optimum protein intake will assist in maintaining or even building muscle mass. Your body can only absorb a certain amount of protein at one time so to get maximum protein absorption, it is important to include some good quality protein-based foods spread throughout the day.

Exercise regularly and include some resistance training

To maintain and build muscle mass, you need to use your muscles! All kinds of exercise will be beneficial to support muscle maintenance; however, resistance training ultimately leads to stimulating muscle growth.

Stay away from fad diets and don’t skip meals

Fad diets, starvation and fasting all work in one way – the restrict the energy (kJ) that you consume; however, if you are not getting enough energy or protein throughout the day to maintain your body processes, your body and your BMR slows down to conserve energy. Long term, restricted energy intake can lead to muscle breakdown. Loss of lean muscle = slower metabolic rate.


Stiegler, P. & Cunliffe, A. (2006).The Role of Diet and Exercise for the Maintenance of Fat-Free Mass and Resting Metabolic Rate During Weight Loss. Sports Med, 36,3, 239-62.
Luke, A. & Schoeller, D.A. (1992). Basal metabolic rate, fat-free mass, and body cell mass during energy restriction. Metabolism, 41, 4, 450-6
Van Gaal, L.F., Vansant, G.A. & De Leeuw, I.H. (1992). Factors determining energy expenditure during very-low-calorie diets. Am J Clin Nutr, 56,1 Suppl, 224S-229S