The belly fat surrounding our organs is considered to be particularly harmful to health – and is the goal of many diet approaches. A team of researchers has now investigated in mice how intermittent fasting affects this visceral fat. It turned out that when the mice alternately fasted for one day and ate for one day, the production of around 1,800 different proteins in their body fat stores changed. While this stimulated fat breakdown in the case of subcutaneous fat, there was a counter-reaction in the case of abdominal fat: This fatty tissue increased the production of fat during intermittent fasting and thus prevented the rapid breakdown.
Intermittent fasting is now considered a promising approach to quickly and permanently lose weight and, above all, fat. Studies also show that this weight-loss concept also has a positive effect on blood sugar metabolism and cholesterol levels. Depending on the model, intermittent fasting can either consist of limiting the time you eat daily – for example, by taking a break from eating for at least 12 to 16 hours overnight. Another variant is fasting on a daily basis: One eats normally for one day, while one with a strong reduction in calories. Alternation schemes with five normal to two days of fasting are also common. These repeated fasting intervals have the effect, among other things, that enzymes and metabolic pathways for fat breakdown are activated in the body, while the new production of adipose tissue is slowed down.
Intermittent fasting changes the proteome of adipose tissue
However, not all fat is the same in our body: the subcutaneous fat tissue under the skin behaves differently in some ways than the visceral fat – the fat that sits in the abdomen and surrounds our internal organs. A third form are the small reserves of brown fat, which are primarily required for the rapid production of heat and energy and which are broken down particularly quickly. Dylan Harney and his colleagues from the University of Sydney have now used mice to investigate how the body’s various fat stores react to intermittent fasting. Specifically, they analyzed the entirety of the proteins that are produced in the adipose tissues during normal fasting and during longer interval fasting. During intermittent fasting, the mice were allowed to eat as much as they wanted for a day, but were given no food for one day.
The analyzes showed: In response to intermittent fasting, the mice showed significant changes in around 1,800 proteins of the adipose tissue. These changes were independent of whether the animal was on a fasting day or a feeding day. In the mice that only fasted once, on the other hand, only around 300 proteins were changed in the fat deposits. “This large difference in the proteome response between intermittent fasting and acute fasting suggests that the repeated fasts in intermittent fasting amplify the changes,” explain Harney and colleagues. They found the greatest changes in proteins that are linked to cell metabolism and, in particular, to the mitochondria. As the researchers explain, this fits in with observations that fasting leads to an increase in mitochondria in white adipose tissue. These in turn are the prerequisite for converting the fat into energy and “burning” it with it.
Belly fat: more fat synthesis instead of more fat loss
At first glance, this suggests that intermittent fasting stimulates fat burning as expected. But on closer analysis, the scientists found clear differences between the reaction of abdominal fat to subcutaneous fat: While the subcutaneous fat actually produced more enzymes for fat breakdown, this was not the case with visceral fat. Instead, a protein that is important for fat dissolution was reduced to a quarter in these fat cells and other enzymes for fat breakdown also decreased instead of increased. On the other hand, the content of the proteins in the visceral fat required for fat build-up increased. “This shows that these fat deposits adapt to intermittent fasting,” write Harney and his team. “Most noticeable is the downregulation of lipolysis and the ramp-up of the metabolic pathways for the synthesis of fatty acids in the visceral adipose tissue.”
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 senior author Mark Larance. “This type of adaptation could be the reason why the belly fat can stubbornly resist losing weight even with longer dieting periods.” Even though they conducted their study with mice, the researchers believe that similar mechanisms are also at work in humans are. 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.
Source: Dylan Harney (University of Sydney) et al., Cell Reports, doi: 10.1016 / j.celrep.2021.108804