Boost Your Metabolism

IN ANY 24hour period, we burn a certain number of calories, known as the total daily energy expenditure (TDEE) and is made up from a number of different types of energy use.

For a start, there is the energy used by the Resting Metabolic Rate (RMR), the amount of calories you burn just to keep alive. This accounts for a big chunk, between 60 and 75 per cent of total daily energy expenditure.

Then there is the Thermic Effect of Feeding (TEF), the extra energy burned during and after eating, which is due to the work involved in absorbing food, digestive enzymes getting busy, increased blood flow and so on.

This takes care of about 10 per cent of daily energy use. Finally, all physical activity, from formal exercise to casual movement such as fidgeting or shivering, uses up calories and generally constitutes between 15 and 30 per cent of daily energy expenditure.

It means exercise increases the calories you use - but by how much? And does it have a longterm impact on your metabolism, when on average women use 2,000 calories a day while men use 2,500 calories?

Post-exercise calorie burn is always of great interest to people wanting to lose weight and scientists have struggled for years to figure out which type of exercise produces the best follow-up burn.

Exercise experts have been fairly certain that strenuous cycling, running and swimming can produce decent post-workout energy expenditures but they have been less confident about strength training. Now, new research carried out at Colorado State University suggests that a strenuous bout of resistance training can produce a postexercise burn which may be a little more intense than that produced by traditional aerobic workouts.

Researchers asked a group of volunteers to participate in a resistance-training workout then a cycling workout on different occasions. Each exercise session was designed to burn 600 calories.

To control the effects of dietary intake on metabolic rate, all volunteers ate similar meals before and after the workouts.

In the five hours following each of the two workouts, calorie burning was significantly higher than normal. There was a difference in calorie expenditure but it wasn't huge - about 24 extra calories burned after strength training.

But before you shift from aerobic workouts to strength training in the hope of getting slimmer, bear in mind that it took the Colorado State strength trainers 100 minutes to burn about 600 calories, while the cyclists accomplished the same thing in slightly over an hour.

AEROBIC EXERCISE Studies have found that aerobic exercise increases energy expenditure in the period of time immediately after activity. But there may be a threshold to clamber over before the effect kicks in. Light aerobic exercise seems less likely to make a difference, while moderate or intense is more likely to do so.

For example, one study found that light exercise led to burning an extra 5-10 calories afterwards;

moderate an extra 12-35 calories.

In contrast, strenuous exercise was shown to increase postexercise energy burning by a huge 180 calories.

Other research has found that any post-exercise increase in RMR fades between 24 and 39 hours later. But the studies to date all point to the fact that to boost energy expenditure significantly after exercise, activity needs to be intense and for more than 50 minutes.

REGULAR EXERCISE Other research has focused on the effect of regular exercise, rather than looking at the immediate effects of a one-off exercise session. Studies have found that metabolic rate is between 5 and 19 per cent higher in highly active regular exercisers compared to irregular exercisers or sedentary individuals.

Dr Catherine Geissler, a nutrition expert at King's College London, estimates that the increased lean body mass associated with exercise can increase total daily energy expenditure by between 7 per cent (143 calories per day) for a moderately active person to 16 per cent (326 calories per day) for a regularly highly active person.

GENDER Sadly, there may be a gender difference in the metabolic response to exercise. At least four studies looking at the energy differences between men and women found that total daily expenditure did not significantly increase following training in women but did in men. It appears that women conserve energy more efficiently (they burn fewer calories) at rest and in response to exercise.

AGE Your age has an effect, too.

One study found that resistance training has an effect on resting metabolic rate (independent of any change in muscle mass) for the over-50s but not in younger individuals, clearly highlighting the importance of resistance training in people aged 50 plus.

DIET So how is the metabolism affected by diet and the energy available from food, measured in calories?

When the amount of energy you take in (calories consumed) is equal to the amount of energy you use up (calories burned), you are said to be in "energy balance".

If you are burning more calories than you eat, you are in "negative balance". Eating more calories than you burn puts you in "positive balance".

A conventional diet aims to make sure you are burning substantially fewer calories than you are consuming, but some experts believe that being in a state of negative energy balance puts your body into a special energyconservation mode.

In other words, the body believes there is a scarcity of calories, and it has to conserve what energy is available.

BURN BOOSTERS The research shows that:

Exercise significantly increases metabolic rate for between six and 36 hours after exercise.

For exercise to be effective, we have to work our heart at more than 70 per cent of its maximum rate.

Exercise has to be regular.

Resistance exercise is a good way to offset the declining metabolic rate typically found as we age.

The perfect weekly workout routine includes both resistance training and aerobic training.