October 23, 2023, 4:23 pm | Read time: 6 minutes

There was a time when food scarcity meant that a few extra pounds were considered a desirable “prosperity belly.” That has since changed: an endless supply in supermarkets and 24/7 fast-food restaurants have caused many people’s waistlines to expand faster than they would like. According to the WHO, overweight and obesity affect nearly 60 percent of adults and almost every third child in Europe.¹ American researchers from the University of Colorado claim to have deciphered the core problem of this epidemic. Their study results suggest that fructose, better known as fruit sugar, is a significant factor in the development of obesity.

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Overweight and Obesity–What Is the Difference?

Obesity is defined as an increase in body fat that exceeds the normal level. The Body Mass Index (BMI) is used to classify body fat. It is the quotient of weight and height squared (kg/m²). Values above the normal weight are classified into overweight and various degrees of obesity²:

• Normal weight: 18.5 to 24.99 kg/m²
• Overweight (pre-obesity): 25 to 29.99 kg/m²
• Obesity Grade 1: 30 to 34.99 kg/m²
• Obesity Grade 2: 35 to 39.99 kg/m²
• Obesity Grade 3: over 40 kg/m²

Both overweight and obesity are known risk factors for diet-related diseases such as Type 2 diabetes, lipid metabolism disorders, and cardiovascular diseases. Additionally, obesity is considered a standalone disease, whereas overweight is not.

In Germany, according to the WHO, 56.8 percent of adults are overweight, of which 22.3 percent are obese. Men are slightly more affected than women.

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The Cause of Obesity Is Multifactorial

There is no single reason why people become obese. Personal lifestyle, psychosocial, and environmental factors all play a role in the development of obesity. In science, there are several models or hypotheses on the development of obesity.

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Hypotheses on the Development of Obesity

A well-known model is the energy balance hypothesis. It describes that the most common reason for excess pounds is a positive energy balance. This means that people consume more energy through food than they need. The body then stores the unused energy as fat tissue.

The protein-leverage hypothesis suggests that the change in the ratio of protein to carbohydrates and fats plays an important role in the amount of energy intake. Accordingly, a person would eat until their protein needs are met. However, if someone eats a low-protein diet, it encourages them to consume more energy than they need.³

The so-called carbohydrate-insulin model is also among the most important hypotheses. It describes that increased carbohydrate intake is associated with increased insulin secretion. As a result, the hormone overshoots its target in fulfilling its task of prompting cells to store sugar. The blood sugar level drops, and the brain believes there is too little energy. To protect us from starvation, the brain switches to energy-saving mode, making us want to move less and crave energy-rich foods.⁴

The authors of the U.S. study consider these hypotheses largely correct. However, it is unclear whether the focus in treating obesity should be on reducing carbohydrate or fat intake or rather on increasing protein intake.⁵

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Researchers Identify Fructose as the Core of All Obesity Hypotheses

According to the study authors, all hypotheses can be unified in the fructose survival hypothesis they researched.

When the body metabolizes fructose, it reduces the active energy known as ATP (adenosine triphosphate), leading to hunger and increased food intake. ATP is understood as the “energy currency” of cells. More specifically, fructose can reset the ATP level in the cell to a lower level by suppressing mitochondrial function while simultaneously blocking the “ATP supply” from body fat reserves. The low intracellular ATP level then leads to increased consumption of fatty, energy-rich foods.

This hypothesis highlights the role of carbohydrates in stimulating food intake, while fat primarily serves as an energy source. Consequently, obesity is a disorder of energy metabolism, where available energy or ATP is low despite increased total energy intake.

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More on the topic

Illness Causes, Symptoms and Consequences of Obesity

According to the study This effect occurs when you consistently drink too little water.

Nutrition Expert Answers: How Can I Reduce My Fructose Intake?

Sources

• 1. World Health Organization (WHO). (2022). WHO European Regional Obesity Report 2022. (accessed on 10/23/2023)
• 2. Deutsche Gesellschaft für Ernährung (DGE). Overweight and Obesity. (accessed on 10/23/2023)
• 3. Gosby, A. K., Conigrave, A.D., Lau, N. S. et al. (2011). Testing protein leverage in lean humans: a randomised controlled experimental study. Plos One.
• 4. Ludwig, D. S., Aronne, L. J., Astrup, A. et al. (2021). The carbohydrate-insulin model: a physiological perspective on the obesity pandemic. The American Journal of Clinical Nutrition.
• 5. Johnson, R. J., Sánchez-Lozada, L. G., Lanaspa, M. A. (2023). The fructose survival hypothesis as a mechanism for unifying the various obesity hypotheses. Obesity.