Overweight is a complicated issue!
The most important take-home message
- Physical activity per se is not necessarily an effective means of weight reduction for all. Nevertheless, it should be emphasized that increased physical activity gives health benefits and reduced risk of the most prevalent chronic diseases and mortality, even without weight reduction.
Other take-home messages
- There is some agreement about the importance of the diet for obesity.
- Physical activity has been reported to reduce weight to a moderate extent (5 – 10% of original body weight, appears to be achievable without calorie restrictions).
- When physical activity is combined with dietary measures, increased activity seems to have an only moderate effect.
- Physical activity is likely to play a key role in maintaining weight loss, in order to “keep weight”.
- We are biologically and genetically engineered for high levels of physical activity and it will, therefore, be easier to adjust the energy intake of energy consumption when we are more physically active.
- If you are less physically active, appetite regulation does not follow, which can result in energy surpluses and weight gain.
- From nature, the body seems to counteract weight reduction to a greater extent than weight gain (compensating for more physical activity with a lower metabolism).
The main reason for overweight is energy surplus over time, where energy intake exceeds energy consumption.
To what extent does physical activity affect body weight?
What advice should we provide as a healthcare provider for physical activity to obese people who want to lose weight?
Overweight is defined by the World Health Organization as body mass index (BMI) > 25 kg/m2, and in 2015 caused overweight approx. four million deaths and 120 million health-impaired lives worldwide. Overweight is rated as the fourth largest risk factor for the global disease burden. There is some agreement about the importance of the diet for obesity, while the meaning of physical activity is more controversial.
Weight reduction
In intervention studies, physical activity has been reported to reduce weight to a moderate extent, and studies have shown an average weight reduction of 1-3 kg over 6-12 months. Weight reduction of clinically relevant size, i.e. 5 – 10% of original body weight, appears to be achievable without calorie restrictions. However, this is assumed to require one-hour moderate intensitive physical activity daily, i.e. activity like fast walking, ball games, cycling to sweat/breathe, or more targeted exercise like running, strength training and aerobics/dance. However, when physical activity is combined with dietary measures, increased activity seems to have an only moderate effect (7-9).
Persistent weight reduction
Physical activity is likely to play a key role in maintaining weight loss, in order to “keep weight”. Both prospective and retrospective studies provide a reason to assume that 60-90 minutes of moderately intensive physical activity daily, equivalent to energy supply of 2 500-2800 kcal per week, increase the likelihood of successful weight regulation over time.
Probably it is easier to maintain energy balance when both energy consumption and energy intake are high. The rationale for this is that we are biologically and genetically engineered for high levels of physical activity and that it will, therefore, be easier to adjust the energy intake of energy consumption when we are more physically active. If you are less physically active, appetite regulation does not follow, which can result in energy surpluses and weight gain.
Metabolic Compensation
From nature, the body seems to counteract weight reduction to a greater extent than weight gain, and by weight reduction, physiological processes (metabolic compensation) are implemented to restore the original weight. It is postulated that total energy consumption is regulated homeostatically and remains relatively stable within a limited range.
Instead of increasing the energy consumption linearly with the physical activity level, the basic metabolic activity decreases when the activity level becomes very high – thus compensating for more physical activity with a lower metabolism. According to this theory, therefore, the increased physical activity does not necessarily lead to a higher total energy consumption.
Behavioral compensation
In addition to metabolic compensation, a higher physical activity level may lead to other behavioral changes. For example, a summary article about a partial compensation of 30% in the form of higher energy intake (participants ate more) was reported in the weeks following an increase in physical activity level. Furthermore, it is estimated that 55 – 64% of increased energy consumption as a result of training interventions is compensated for, either through increased energy intake, lower total physical activity level, or a combination of both.
Short-term and long-term effect
Today’s knowledge about weight reduction indicates that one should distinguish between short-term and long-term effects of higher physical activity levels. In the short term, i.e. after a workout, the likely higher level of physical activity will affect appetite regulation by getting faster satisfied at the next meal due to increased sensitivity to key hormones like leptin and insulin.
However, increased physical activity over time appears to have a two-sided effect. On the one hand, a change in body composition, in the form of less fat and a greater proportion of fat-free mass, can result in higher residual metabolism and higher total energy consumption, which can increase energy intake. On the other hand, less fat and more fat-free mass can also increase insulin sensitivity and improve appetite regulation, and thus not necessarily a higher energy intake.
Individual variations
However, the differences between individuals are high. In a study, it was found that after a training session over 12 weeks the average weight reduction was 3.7 kg. Nevertheless, there was a spread in the range from -14.7 kg to + 1.7 kg, of which four participants (11%) gained weight. These four compensated in terms of increased energy intake and thus experienced less weight reduction than calculated from the increased energy consumption from the exercise. Nevertheless, it was pointed out that the increase in physical activity levels resulted in other key health effects – including those who compensated for eating more, such as reduced body weight, lower blood pressure and resting heart rate and higher oxygen uptake.
In short, the underlying mechanisms that regulate the relationship between physical activity and weight reduction are very complex, and with significant individual variations. Physical activity per se is therefore not necessarily an effective means of weight reduction for all. Nevertheless, it should be emphasized that increased physical activity gives health benefits and reduced risk of the most prevalent chronic diseases and mortality, even without weight reduction.
References
- How your body fights back when you diet
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N Engl J Med. 2017 Jul 6;377(1):13-27. doi: 10.1056/NEJMoa1614362. Epub 2017 Jun 12.Health Effects of Overweight and Obesity in 195 Countries over 25 Years.
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Lancet. 2016 Oct 8;388(10053):1659-1724. doi: 10.1016/S0140-6736(16)31679-8.Global, regional, and national comparative risk assessment of 79 behavioral, environmental and occupational, and metabolic risks or clusters of risks, 1990-2015: a systematic analysis of the Global Burden of Disease Study 2015.
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Surg Obes Relat Dis. 2017 Oct;13(10):1643-1650. doi: 10.1016/j.soard.2017.08.002. Epub 2017 Aug 12. Obesity in America.
About the Author Kjell H Kjellevold
A doctor and specialist in pathology. He has always been concerned about health and how to manage a good and healthy lifestyle. The blog will mainly be about the use of essential oils, health, and training.
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