Fat cells – Better than their reputation

29 Nov 2021

“A healthy person can cope with unhealthy fats, too,” Alexander Bartelt says. The LMU Professor of Cardiovascular Metabolism is conducting research into why people gain weight – and how losing weight works.

© picture alliance / Felbert+Eickenberg / STOCK4B / VisualEyze

At the Institute for Cardiovascular Prevention, Professor Alexander Bartelt’s research focuses primarily on the metabolic processes in brown adipose tissue. His work in this field has already won him an ERC Starting Grant from the European Research Council (ERC). And his research topic makes him a popular interview partner on issues relating to overweight and weight loss.

What did the lockdowns do to the German’s body weight?

Alexander Bartelt: In the first half of 2020, every one of us put on a kilogram on average. Obese people actually put on 7.5 kilograms – and those are only the average figures. To put it bluntly: The Germans are too fat, though there are clear differences based on educational status, income and region. People in cities are thinner than those in the country, for example. Above all, however, children are growing ever fatter and were unable to pursue their hobbies during lockdown. The longer they stay overweight, the greater the risk that they will suffer metabolic diseases later in life.


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Studies indicate that 160,000 deaths a year in Germany are attributable to too much fat, salt and sugar. Why does the government not take a harder line on this matter?

Because it is not so easy to define the cause of death. No one dies because they are too fat. Being fat is merely a risk factor for diabetes, heart attacks and strokes. So, since you will never read anything about overweight in the statistics, the problem tends to fly under the political radar. As a health researcher, I can only exhort [the government] to take this issue seriously. Statistically, every second person is overweight – a number that is rising sharply. These are terrifying figures.

So, losing weight is not as easy as slim people imagine?

Our energy metabolism has been optimized by evolution but is now confronted by modern life – a dangerous mix. This means that, to lose weight, we have to fight against our body’s own biology, which desperately wants to keep extra calories for later. Eating less and getting more exercise is much more difficult than it sounds, and there are so far only a few effective medications on the market for obese people. The ultimate measures involve stomach reduction, gastric bands, and stomach bypasses. That said, there is a biological reason why we have fat cells – they have a metabolic purpose, which means that being extremely thin is not desirable either.

You mean a little bit of fat here and there can be a good thing?

Yes, it can. In our society, fat cells are seriously underestimated or misunderstood. There are many fats that our body itself cannot produce, so it needs to get them from what we eat. A healthy person can cope with unhealthy fats, too: They can metabolize them, break them down or excrete them. But these days we absorb far too many calories – not just from fat, but also from sugar, glucose and above all fructose. And although our fat cells are effectively as flexible as balloons, they will overflow if this becomes a permanent state.

In your book “Der Fettversteher” (“The Fat Whisperer”), you write that fat cells can be happy or aggressive.

A happy fat cell is well filled, has sufficient oxygen, and is surrounded by nice neighbors, by which I mean other happy fat cells. If we eat too much, the fat cells get too full. They then become aggressive and start throwing inflammatory molecules around. That attracts cells from the immune system, and the fatty tissue becomes chronically inflamed. The fat cells thus lose their protective metabolic function and overflow, causing the fat to spill over into the blood, to the liver, and other organs. At this point, healthy stores of fat become a concomitant source of illness.

You have found a mechanism that constantly regenerates fat cells from the inside. For this discovery, you received the research award of the Deutsche Adipositas-Gesellschaft, DAG (the German Obesity Society) in November. Is this the key to a lifelong perfect figure?

At best, it is one piece of the puzzle. We are very interested in brown fat cells in humans, of which not even the scientific community is fully aware yet. To put it simply: When we feel cold, the brain tells the brown adipose tissue: “I’m cold - Warm me up.” This process, known as thermogenesis, requires a lot of energy, which is why it disspates lots of fat, sugar and other energy-rich molecules. Mice that are exposed to cold overnight lose weight rapidly. We still know relatively little about this process in humans, but the knowledge gap creates opportunities for new discoveries.


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In other words, freezing helps you lose weight?

In principle, yes! Most people are reluctant to leave their temperature comfort zone. You don’t have to plunge straight into an ice bath, although doing so activates the brown fat. But even if you go for a walk without wearing a jacket, your brown fat burns calories. However, only 0.02 percent of an adult’s bodyweight consists of brown fat cells. So, it is not enough just to leave the window open overnight, even though that might get rid of a kilogram of fat per year. Cold showers can also be helpful, as can spices such as chili and even caffeine in the form of capsules, for example.

What good are diets and liposuction?

Most diets help, but only in the short term. The same goes for liposuction. As soon as you go back to eating as you did before, the yoyo effect inevitably sets in. No one wants to go on a cabbage diet for the rest of their life. The only thing that helps is knowing your own eating habits, analyzing them, and looking for lasting ways to change them – be that a low-carb or protein-free approach. The most important thing is the number of calories, as even too much fruit can be a bad thing. Natural foods are always more helpful than processed foods, i.e. apples rather than apple juice, whole grain bread with whole grains rather than soft bread from fine-ground flour.

What a pity that the supermarket shelves have been full of chocolate Santas for weeks to tempt us. Do you have any clever hints?

Seasonal treats are especially appealing. They trigger pleasurable sensations in the body like many other drugs, but these ones are legal. To avoid binge eating, the only thing I can advise lovers of Christmas cookies is to buy just a small pack instead of the two-kilogram box. To guard against an over-intake of calories, I would generally like to see the Nutri-Score – the five-color nutrition label – on all products. Sadly, that is not yet compulsory in Germany.

Professor Alexander Bartelt

Knows a thing or two about fat: Alexander Bartelt. | © privat

The Germans tend to gain most weight over the Christmas season. How can they stay in good shape despite all the evening meals?

Christmas is a classic example of social eating, where we eat more than we actually need because that is what the social occasion demands. I don’t have any good advice here, other than that you could maybe skip dessert and not drink so much alcohol – that is all extra calories. On the other hand, I wouldn’t switch to salad only. (laughs) Instead, how about hopping on your bike over the festive season instead of taking the train? In the past, we only had this kind of feast once or twice a year, but today we much more frequently eat more than we need to. And you can find food on every street corner.

How hard do you personally find it to maintain a steady weight?

Unfortunately, it is not necessarily easier for me either. I may be slim, but not even I fit in the suit I wore ten years ago. My research obviously helps me avoid getting too worked up about some things. To a certain extent, it is normal and good for your body to round out as you get older. People are fat by nature – that is something we must accept. But sufficient exercise and sport will keep your metabolism working well, allowing you to get through life just fine even without your ideal body-mass index.

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