In a mouse study, Australian researchers found what goes on behind the scenes of adipose tissue during intermittent fasting and showed that it triggers a cascade of dramatic changes, depending on the type of fat deposits and where they are in the body.
Using state-of-the-art instruments, researchers at the University of Sydney found that fat around the stomach, which in humans can build up into a “protruding belly”, goes into “preservation mode”, adapts over time and becomes more resilient to weight loss.
The results are published today in Cell Reports.
One of Dr. Mark Larance-led research team studied adipose tissue types in different locations to understand their role in alternate-day fasting with no food consumed on alternate days.
Types of fat that were seen to change included visceral “belly” fat, which is the fatty tissue that surrounds our organs, including the stomach, and subcutaneous fat, which lies just under the skin and is associated with better metabolic health is.
“While most people would think that all adipose tissue is the same, location actually makes a huge difference,” said senior author Dr. Larance from the Charles Perkins Center and the School of Life and Environmental Sciences at the University of Sydney.
“Our data shows that both visceral and subcutaneous fat experience dramatic changes during intermittent fasting,” said Dr. Larance, who is also an NSW Future Research Fellow’s cancer institute.
Why Visceral Fat Can Be Resistant to Weight Loss
During fasting, adipose tissue supplies the rest of the body with energy by releasing fatty acid molecules.
However, the researchers found that visceral fat became resistant to this release of fatty acids during fasting.
There was also evidence that visceral and subcutaneous fat increased their ability to store energy as fat, which likely resulted in fat stores being quickly rebuilt before the next period of fasting.
Dr. Larance said it was possible that a history of repeated fasts triggered a maintenance pathway in visceral fat.
“This suggests that visceral fat can adapt to repeated fasting attacks and protect its energy stores,” he said.
“This type of adjustment may be why visceral fat can become resistant to weight loss after long periods of diet.”
Dr. Larance said using a mouse model was a useful analogue to pre-human studies.
“The physiology of mice is similar to that of humans, but their metabolism is much faster, so we can see changes faster than human experiments and examine tissues that are difficult to extract in humans,” he said.
Future research in mice and humans could reveal the mechanisms by which this resistance occurs, as well as what types of diets and other interventions are best for controlling belly fat.
Mapping of the inner workings of fat deposits
The research team examined more than 8,500 proteins in fat deposits and, using a technique known as proteomics, compiled a catalog of changes that occurred during intermittent fasting.
Proteomics – the study of all proteins – a relatively new field of study, which takes its name from genomics (the study of all genes), monitors how proteins react under certain conditions, which in this case is intermittent fasting.
The results provide a rich source of data that will help paint a more complete picture of the inner workings of adipose tissue.
Through proteomics, the research team was made aware of important cellular changes caused by intermittent fasting and, after further analysis, highlighted the mechanism of action of visceral fat in action.
The study was carried out using the Sydney Mass Spectrometry instruments at the Charles Perkins Center, which is part of the University of Sydney’s nuclear research facilities.
Dr. Larance says it should be noted that the intermittent study results may not apply to various diet regimens such as the 5: 2 diet (fasting 2 out of 7 days) or the calorie restriction that is common in people looking to lose weight.
The results form the basis for future studies to examine the molecules responsible for why visceral fat is resistant to energy release during fasting and to identify which diet plans are most beneficial for metabolic health.
“This type of research was made possible by these new tools that allow us to look beyond the street lamp – it’s a hypothesis that generates; we knew we were going to find something, but we didn’t know what,” explained Dr. Larance.
“Now that we’ve shown that ‘belly fat’ in mice is resistant to this diet, the big question will be, why and how do we best go about it?”