The physiological basis behind weight loss is simple: you need to ingest fewer calories than you expend daily to promote a negative daily energy balance, which continues over a period of time.

On the other hand, for a successful weight loss process, it is very important to be monitored by a registered dietitian, who will prescribe you a personalised diet plan according to your tastes and needs, as adherence to the plan is a key factor for success. ⁽¹⁾

However, one of the issues most associated with the difficulty of losing weight is ‘slow metabolism’. But what is ‘metabolism’ and what role does it play in weight loss?

 

Deconstructing metabolism

Overall, metabolism represents the set of chemical processes and reactions that take place in our bodies with the ultimate goal of producing energy.

However, when we talk about metabolism in the context of weight loss, we are usually referring to daily energy expenditure, i.e. the number of calories we burn each day. ⁽²⁾

This energy expenditure can be divided into 3 components: basal metabolic rate, physical activity and the thermic effect of food.

1. Basal Metabolic Rate

The Basal Metabolic Rate is the most significant component of metabolism and represents the energy expended to maintain the body's vital functions (it contributes around 70% of daily energy expenditure).

This expenditure is directly related to age, gender, weight and body composition: for example, muscle mass is a more metabolically active tissue than fat mass (13 kcal/kg/day vs 4.5 kcal/kg/day, respectively), so the greater the weight of muscle mass in our body, the greater the basal metabolic rate and, consequently, the greater the daily energy expenditure.

On the other hand, this expenditure tends to be higher in men and decreases with age.

It's also important to emphasise that, in weight loss processes, this basal metabolic expenditure tends to decrease with the duration of energy restriction, which is a natural metabolic adaptation of the body that slows down and makes the results non-linear. ^(2,3)

2. Physical Activity

This portion represents the expenditure from programmed physical exercise (e.g. gym or any sport) and the expenditure associated with other spontaneous day-to-day activities, such as chewing, sitting and standing, walking, among others, which is higher than the energy expenditure at rest.

This figure is also influenced by our body composition and level of muscular efficiency ^(2).

3. Thermic effect of food

Finally, the thermic effect of food refers to the energy expended in the processes of digestion and absorption of the food ingested. Protein is the nutrient with the greatest thermic effect (20-30%), followed by carbohydrates (5-10%) and fat (0-3%).

In this context, and although the consumption of protein-rich foods does not substantially increase daily calorific expenditure in weight loss processes, it may be interesting to increase protein intake if it is low in relation to your nutritional needs.

Furthermore, a higher protein intake can also help improve appetite control and body composition ^(4).

 

So what's the relationship between metabolism and weight loss?

As mentioned above, the most important aspect of weight loss is energy intake. This should be lower than your total daily energy expenditure, regardless of the efficiency of your metabolism.

If your metabolism is ‘faster’ / ‘more efficient’, this means that you will burn more calories at rest and during physical activity. This is one reason why some people can eat more than others without gaining weight.

However, contrary to what you might think, overweight people generally have a higher metabolic rate, as they have more tissue and need more energy to trigger basic processes such as breathing.

However, as their food intake is higher than their total expenditure, weight gain continues to occur. ⁽²⁾

 

Conclusion

In this sense, the best way to optimise your weight loss and metabolism is to reduce your energy intake, favour foods with a higher protein content, especially if your usual intake is low, and increase your daily physical activity.

By practising more physical exercise combined with an adjusted protein intake, you'll also boost your muscle mass gain and, consequently, your metabolism.

 

Bibliography

1. Thom G, Lean M. Is There an Optimal Diet for Weight Management and Metabolic Health? 2017 May;152(7):1739-1751. doi: 10.1053/j.gastro.2017.01.056. Epub 2017 Feb 15. PMID: 28214525.
2. The truth about metabolism. Harvard Health. (2024, July 23). https://www.health.harvard.edu/staying-healthy/the-truth-about-metabolism
3. Casanova, N., et al. (2019). Metabolic adaptations during negative energy balance and their potential impact on appetite and food intake. Disponível em: https://www.ncbi.nlm.nih.gov/pubmed/30777142
4. Calcagno, M., Kahleova, H., Alwarith, J., Burgess, N. N., Flores, R. A., Busta, M. L., & Barnard, N. D. (2019). The Thermic Effect of Food: A Review. Journal of the American College of Nutrition, 38(6), 547–551. https://doi.org/10.1080/07315724.2018.1552544

 

Author:

Rita Lima (CP.3003N)