Why are more people becoming obese?

We live in an obesity pandemic

Rising obesity rates are one of the biggest health challenges of the 21st century. According to the World Health Organisation (WHO), one in eight people is obese - that's around 1 billion people worldwide. While the adult obesity rate has doubled since 1990, the rate among children and adolescents aged 5 to 19 has quadrupled [WHO, 2024]. The reasons for the rising numbers are many, but those affected often face stigma and prejudice [Friedman, 2004].

A major reason for the rising obesity rate is the persistent imbalance between the amount of calories we eat and the amount of calories we burn [Boutari et al., 2023]. This imbalance results in more energy being consumed than expended, known as a positive energy balance. This positive energy balance is influenced by two main factors: diet and exercise [Malik et al, 2013].

Diet

Our diet plays a significant role in the rise in obesity rates. A key factor is the previously mentioned positive energy balance - more energy is taken in through food than is used - which is largely due to the abundance of food.
In Western countries, everything is generally available in abundance. As a result, more food is consumed than is needed, with excess calories being stored as fat. Diets are also often high in processed foods, which are high in calories, sugar and fat but low in important nutrients such as fibre, vitamins and minerals. Excessive consumption of such foods also contributes significantly to the increase in daily calorie intake [Malik et al, 2013]. The German Nutrition Society recommends a balanced diet rich in fruit and vegetables, whole grains, legumes, nuts and vegetable oils.

For more information on nutrition, visit the German Nutrition Society website.

Physical activity

A lack of physical activity combined with an abundance of foods high in fat and sugar leads to fewer calories being burned than taken in. According to the Robert Koch Institute (RKI), fewer people in Germany are achieving the minimum level of physical activity recommended by the WHO. Between 2014 and 2017, only 26% of children and adolescents aged 3 to 17 were sufficiently physically active (60 minutes per day) [Finger et al., 2018]. A survey conducted by the RKI in 2019/20 found that only about 44% of women and about 51% of men met the WHO recommendation for endurance activity [Richter et al., 2021].

For more information on physical activity, visit the World Health Organization website.

Obesity can lead to changes in our brain

Our decisions regarding food intake and physical activity are also significantly influenced by intrinsic motivation. The motivation to engage in a particular action depends on the extent to which the expected reward outweighs the effort [Hanssen et al., 2022]. The dopaminergic system in the brain plays a pivotal role in regulating motivation and reward. Dopamine is released in response to the sight of a reward, such as food, and is responsible for triggering feelings of happiness. An increasing number of studies indicates that obesity can lead to changes in the dopaminergic system, which in turn may affect motivation [Hanssen et al., 2022].

Experiments on rats have demonstrated that already the consumption of a high-fat diet can result in a diminished appreciation of standard food. The reason for this is a reduced release of dopamine when eating standard diet. Consequently, the animals exhibited a reduced motivation to consume low-fat food, as it triggered a lower sense of happiness [Adams et al., 2015]. An experiment in which participants had to engage in physical exertion in order to receive a reward demonstrated the differences in motivation between individuals with a normal weight and those with obesity. Individuals with obesity exhibited a reduced willingness to engage in physical exertion for the purpose of obtaining a reward [Mathar et al., 2016].

A study conducted by the Max Planck Institute for Metabolism Research examined the effects of a high-fat and high-sugar diet over an eight-week period. The findings demonstrated that the preference for such a diet can be altered relatively rapidly. The test subjects were divided into two groups for the purposes of the study. One cohort was provided with a high-fat, high-sugar pudding on a daily basis, while the other cohort was given a lower-fat, lower-sugar pudding with an identical number of calories. Following the eight-week period, it was demonstrated that the test subjects who consumed the high-fat and high-sugar pudding exhibited a heightened response to images depicting high-fat and high-sugar foods. The researchers employed neuroimaging techniques to assess the activity of specific brain regions, identifying a pronounced activation of the dopaminergic system. The high-fat and high-sugar foods had a more rewarding effect on the test subjects than the low-fat and low-sugar pudding [Thanarajah et al., 2023].

Further information regarding this experiment and the impact of sugar on the brain can be found here.

It can be concluded that dietary intake can influence wiring of the brain. A diet comprising a high proportion of fat and sugar can result in alterations in the dopaminergic system, which may in turn give rise to a shift in motivation and an enhanced preference towards the consumption of these foods. The alterations of the brain make it more challenging to refrain from consuming foods with high sugar and fat content. This, in turn, contributes to the rising prevalence of obesity.

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