What is a healthy weight?

The obesity epidemic

Worldwide, obesity has become one of the most important health issues with about 1.9 billion adults being overweight and more than 650 million people being obese (WHO 2016).

The prevalence of obesity in adults in the United States of America is more than 40% (2017-2018 CDC) and various efforts exist to address this health issue.

Nevertheless, the prevalence of obesity and overweight people is steadily increasing. Importantly, obesity is a major risk factor for diseases such as type 2 diabetes, cardiovascular diseases, and several types of cancer.

What is a healthy weight?

A healthy weight can be defined as the weight causing the lowest death rates (or severe health issues) when examining large cohorts of people.

However, the individual healthy weight depends on several factors such as height, gender, age, lean body mass, and sporting activity.

How can we measure healthy weight?

The next important step is to ask how can we quantify healthy weight as accurate and reproducible as possible.

Besides the bodyweight itself, the body mass index (BMI), the waist circumference, and the waist/hip ratio are helpful parameters:

• The most commonly used method to diagnose obesity is the BMI (first described in the 19th century and calculated as the weight in kilograms divided by the height in meters squared).
• Normal weight ranges from BMI 18.5-24.9, even though there is evidence that in a few individuals harmful effects can already occur at lower values such as 22-23.
• Overweight is defined as BMI 25–29.9 and the different degrees of obesity begin with BMI 30 and above. However, these reference ranges may need to be adjusted for different ethnic groups. A limitation of the BMI is the missing capability to differentiate body fat from lean body mass (e.g. muscles).
• Waist circumference and waist/hip ratio are often used to measure central obesity to get an idea about the amount of visceral adipose tissue.
• From a clinical point of view, visceral adipose tissue is known to be especially harmful and its amount is a good measure for the risk to develop metabolic syndrome, type 2 diabetes, cardiovascular disease, hypertension, and dyslipidemias.
• It is also correlated to increased all‐cause mortality. Waist circumference is easy to measure and seems to be an even better predictor for future medical care costs than BMI.

Why do we gain weight?

• The quality and quantity of ingested food affect body weight.
• There is a genetic predisposition to gain weight and also the localization of fat depots is at least in part determined by genetics.
• Lifestyle and physical activity: Lack of physical activity decreases energy expenditure and therefore the working metabolic rate.
• Age is often accompanied by loss of e.g. muscle mass and basal metabolic rate decreases over time.
• In the cultural and social environment, there are many reasons to eat regardless of the actual feeling of hunger.
• Some species of gut microbiota from the microbiome can cause inflammation or are very effective to release energy from food sources, which favours weight gain, respectively.

Different types of diets

Low-fat diets

These aim to reduce calories from fat in general. To date, it is suggested that a higher percentage of fat associated calories does not increase the body weight.

There is evidence that reducing the share of fat calories even can result in weight gain. Healthy fats are an important part of a healthy diet.

Low-carb diets

These aim to reduce the number of carbohydrate calories and therefore the curve of insulin release after eating is flattened. The high protein content of the food slows down the movement through the gastrointestinal tract.

Nevertheless, high protein content can cause problems regarding pre-damaged kidneys and it is important to choose foods containing healthy proteins as well as healthy fats to avoid adverse effects and promote health.

Low-glycaemic

These diets aim to attenuate the rise of blood sugar levels and therefore insulin response by choosing food with a low-glycaemic index and glycemic load.

In many cases, both parameters are lower in unprocessed food (e.g. whole grains with high fibre content) and it can be recommended to limit the intake of highly processed sources of carbohydrates. If the insulin response is weaker, the blood sugar is removed more slowly and hunger feeling occurs later.

Steps to control weight

• It is important to find an eating strategy that is individually manageable in the long term. A diversified diet including good sources of high-quality healthy fats, carbohydrates, and proteins is often suitable, preferably in combination with other health-promoting ingredients such as e.g. micro-nutrients, vitamins, and polyphenols.
• It is helpful to avoid calories from beverages and desserts as well as oversized portions.
• Exercise increases energy expenditure and therefore ultimately weight loss. Additionally, there is a large body of evidence that exercise is important to maintain health, for example, by strengthening the immune system.

Author: Dr Markus Burkard