Metabolism: What is it and how can you activate it?

Metabolism is a term that means all the chemical reactions in our body. These chemical reactions keep the body alive and functioning. However, the word metabolism often implies the metabolic rate, ie the number of calories we burn. The higher the metabolic rate, the more calories we burn and the easier it is to lose weight or maintain a reduced weight.

The basic metabolic rate is the calories needed for the body to function at rest, when we are resting or sleeping. It accounts for about 60-65% of total energy expenditure. Basic metabolism does not take into account the calories we need for everything else we do, such as movement (25-30%), thinking and digesting food (5-10%). Total energy expenditure combines the calories we need at rest plus the calories for activities.

Metabolism is often reduced when we diet. In this way the body resists the reduction of its weight. Why this happens is not clear but it is believed to be an ancient mechanism. When the first cells that appeared on Earth could not find food, they survived by reducing their energy expenditure. This mechanism helped mammals survive glacial periods and is still preserved in animals and humans.

How is metabolism activated?

Here are some ways in which the metabolism can be activated and the problem of reducing it can be overcome when dieting.

1. Eat more protein

Eating food can increase our metabolism for a few hours. This is called the thermal effect of food (TEF) or trophic thermogenesis. It is caused by the extra calories needed to digest, absorb and process food. Protein digestion requires a higher calorie expenditure. Food thermogenesis when consuming proteins increases the metabolic rate by 15-30%, compared to 5-10% for carbohydrates and 0-3% for fats [1].

Also, when we eat more protein, we are more likely to consume fewer calories. One study found that participants were likely to consume about 440 fewer calories per day when protein was increased from 15% to 30% of the total diet with a steady carbohydrate intake and a corresponding reduction in fat. The researchers wrote that the reduction in calorie intake may be caused by increased central nervous system sensitivity to leptin, a hormone that plays an important role in saturating hunger [2].

2. Drink more water

People who drink water instead of sugary drinks are easier to lose weight. It is a fact that sugary drinks contain calories, so replacing them with water automatically reduces calorie intake. However, drinking water can also temporarily speed up metabolism [3].

Studies have shown that consuming half a liter of water increases basal metabolism by 10-30% for about an hour [4]. This calorie burning effect can be even greater with cold water, as the body uses energy to heat it to body temperature [5]. Water can also cause greater satiety of hunger when consumed before meals.

3. Exercise vigorously and lift weights

High-intensity interval training involves rapid and intense outbursts of activity. It can help burn fat by increasing the metabolic rate, even after completing exercise [6]. A study in overweight young men found that 12 weeks of this type of exercise reduced body fat by 2 pounds and belly fat by 17%.

Exercise with weights also activates the metabolism. This means that we burn more calories every day, even at rest [7]. Lifting weights helps maintain muscle mass and fights the drop in metabolism that can occur with weight loss. In one study, 48 overweight women followed a 800-calorie-a-day diet, while some did simultaneous aerobic exercise or resistance training. Those who exercised with resistance maintained their muscle mass, metabolism and strength. The others lost weight, but at the same time lost muscle mass and showed a decrease in their metabolism [8].

4. Drink green tea or coffee

Green tea has been shown to increase metabolism by 4-5% in some studies but not in all. It helps to convert stored fat into free fatty acids and thus increases fat burning by 10-17% [9]. It is believed that green tea can activate our metabolism when we diet.

Caffeine can also boost metabolism by 3-11%. Like green tea, it promotes fat burning. However, this seems to affect the weaker ones more. In one study, coffee increased fat burning by 29% in lean women and only 10% in obese women [10].

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References

1. A high-protein diet for reducing body fat: mechanisms and possible caveats.
2. A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations.
3. Effect of ‘water induced thermogenesis’ on body weight, body mass index and body composition of overweight subjects.
4. Water drinking induces thermogenesis through osmosensitive mechanisms.
5. Water-induced thermogenesis reconsidered: the effects of osmolality and water temperature on energy expenditure after drinking.
6. Oxygen consumption, substrate oxidation, and blood pressure following sprint interval exercise.
7. Contributing factors and variability of energy expenditure in non-obese, obese, and post-obese adolescents.
8. Resistance training conserves fat-free mass and resting energy expenditure following weight loss.
9. Green tea extract ingestion, fat oxidation, and glucose tolerance in healthy humans.
10. Effects of caffeine on energy metabolism, heart rate, and methylxanthine metabolism in lean and obese women.