There are various factors that affect metabolism. This draws much interest in the fat loss community as a bad metabolism is often blamed for an inability to lose fat. There are different factors that affect how many calories per day you need (your metabolism).

Size of the body

The size of the body will determine how many calories you need in general. A large framed guy will need more calories than a tiny woman. The larger organs, muscles and frame require more food to maintain it. This is obvious and at the base of the factors that affect metabolic need.

Efficiency of the body

Your metabolism has a potential to lower its function greatly. Some studies have shown up to 80% of the calorie intake of metabolism is down to pure biochemical processes within the body. The brain has the ability to shut down many of these processes to conserve energy such as in times of famine. Therefore the strength of your metabolism is related to how efficiently you are using what you have been given.


The thyroid goes hand in hand with talks of nutrition and metabolism. The influence on metabolism though is not as great as perhaps its reputation with some studies showing it is responsible for only 10% of total calorie expenditure. This element contributes to the efficiency of your body.

Prior Nutrition

Your food will influence your current metabolic strength. The less you eat, the less calories you will use as the efficiency of the body is reduced. Likewise, the more you eat, the more calories your body will begin to use. This may be due to Leptin or other hormonal influences. Stimulants also have an effect on the body though like the influence of Thyroid they have a small overall contribution. I discussed this previously when I looked at fat burners. Personal experience has shown me that foods that are sensitive to the body also slow and impair your metabolism though  have yet to discover if that is an anecdotal or scientific statement.


A big factor involved in energy use is the temperature of the body and the outside environment. When metabolism slows your resting body temperature may also reduce. In times of cold, if you are outside and exposed to it, the calorie demand for the body can greatly increase.

Movement and exercise.

The effect on metabolism can get a little confusing in regards to exercise, metabolism per se is how many calories your body needs without moving. Metabolism at a practical level of course is the total amount of calories needed including movement. Exercise can decrease metabolism if it corresponds with too large a calorie deficit (as it mimics famine) or it can promote metabolism through raising your basal metabolic rate. Actual daily calorific burn can be significantly increased though extra movement via low or high intensity aerobic or resistance training activities.

Practical applications

The main understanding to take from this is that the calorie demands of your body may vary greatly compared to the next person. To this it is important to be aware that your metabolism and calorie demand will diminish through periods of prolonged dieting. This is neither good nor bad but more a fact of dieting life. The reverse will also happen in that you will increase your calorie thresholds during periods of higher eating. Though factors can increase metabolism the two largest influences for someone trying to lose fat would be temperature and movement. Other factors have a much smaller influence. Likewise, you cannot control the outside temperature so your focus should be on the classic formula of moving while limiting food intake. How much of each to do I have discussed in how many calories do you need and calorie threshold articles.


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