Intermittent fasting reduces lower abdominal fat

Intermittent fasting: Belly fat remains stubborn

Intermittent fasting is a tried and tested remedy for fat deposits. But of all things, the particularly unhealthy belly fat can apparently withstand this alternating fasting - and even actively counteract it. Researchers have now found evidence of this in protein analyzes of the adipose tissue of intermittent fasting mice. While fat loss was boosted in the case of subcutaneous fat, fat production increased in the case of abdominal fat.

Intermittent fasting is said to be particularly effective and long-term aid in losing weight and also has positive effects on blood sugar metabolism and cholesterol levels. With this type of diet, you either have regular fasting days or you limit the time you eat daily - for example, by taking a break from eating for at least 12 to 16 hours overnight.

The repeated fasting intervals should, among other things, have the effect that enzymes and metabolic pathways for fat breakdown are ramped up, while the new production of adipose tissue is slowed down. At the same time, you want to prevent the dreaded yo-yo effect by inserting normal eating phases.

How do the fat deposits react to intermittent fasting?

Dylan Harney and his colleagues at the University of Sydney have now investigated whether this works and how intermittent fasting affects adipose tissue using mice. "The physiology of mice is similar to that of humans, but their metabolism is faster," explains study director Mark Larance from the University of Sydney. "This enables us to recognize changes faster than in humans and also to remove tissue better."

For their study, the researchers analyzed all of the proteins in the fatty tissues of the mice - both in the abdominal fat and in the subcutaneous fat. They compared how the proteome of these fat deposits changes if the mice fasted once or if they did intermittent fasting for a longer period of time. The animals were allowed to eat as much as they wanted for a day, but were given no food for one day.

Intermittent fasting changes the proteome

The result: In response to intermittent fasting, the mice showed significant changes in around 1,800 proteins in adipose tissue. In the mice that only fasted once, on the other hand, only around 300 proteins were changed in the fat deposits. "This large difference between intermittent fasting and acute fasting suggests that the repeated fasts of intermittent fasting increase the proteome response," write Larance and colleagues.

They found the greatest changes in proteins that are linked to cell metabolism and the mitochondria. This fits in with observations that fasting leads to an increase in mitochondria in white adipose tissue. These are the prerequisites for converting the fat into energy and using it to "burn" it, as the researchers explain. At first glance, therefore, the protein changes suggest that intermittent fasting stimulates fat burning, as expected.

Belly fat switches to fat production instead of degradation

But this picture is deceptive, as closer analyzes revealed: While the subcutaneous fat tissue actually produced more enzymes for fat breakdown, this was not the case with abdominal fat. Instead, a protein that is important for fat dissolution was reduced by a factor of four and other enzymes for fat breakdown also decreased instead of increased. On the other hand, the content of the proteins required for fat build-up in this visceral fat increased.

“This shows that these fat deposits adapt to intermittent fasting,” explain the scientists. "Most noticeable in visceral adipose tissue is the downregulation of fat dissolving and the ramping up of the metabolic pathways for the synthesis of fatty acids."

“Economy mode” as a backlash

According to the researchers, this suggests that the belly fat in particular switches to a kind of economy mode during intermittent fasting: "The visceral fat can apparently adapt to repeated fasting periods and protect its energy supply," explains Larance. "This type of adjustment could be the reason why belly fat can stubbornly resist losing weight, even with lengthy diets."

Even though they conducted their study with mice, the researchers believe it is likely that similar mechanisms could also be at work in humans. Whether this undesirable adjustment effect of the belly fat also occurs in other intermittent fasting models remains to be investigated.

"Now that we've shown that belly fat in mice can become resistant to this form of diet, the big question is why that is and how best to prevent it," says Larance. (Cell Reports, 2021; doi: 10.1016 / j.celrep.2021.108804)

Source: University of Sydney

March 3, 2021

- Nadja Podbregar