A recent Australian study poses concerns about intermittent fasting efficacy in reducing belly fat after discovering that the tissue grew immune to weight loss.
The effects of every-other-day fasting, in which no food is eaten on alternating days, on various fat tissue in mice were studied in a review released on Wednesday in Cell Reports by the University of Sydney.
When people fast, visceral fat - the abdominal fat that covers organs and can create a protruding tummy - goes into "preservation mode" and adapts to be more immune to weight loss.
When you fast, the body begins to burn fat tissue instead of glucose from food. You'd imagine that all fat tissue is the same and that location doesn't matter.
But according to ZME Science, researchers discovered that this isn't the case. In fact, Forbes said intermittent fasting might make shedding belly fat more complicated.
"This was unexpected," says lead author Dr. Mark Larance, of the Charles Perkins Centre. "[It shows] diets can affect different fat depots differently," he told Sydney Morning Herald.
Mapping Out How Fat Deposit Works
In the study titled "Proteomics Analysis of Adipose Depots After Intermittent Fasting Reveals Visceral Fat Preservation Mechanisms," researchers analyzed different forms of fat tissue from various positions on mice's bodies in order to better understand their function during every-other-day fasting, in which no food is eaten on alternating days.
The researchers used a mass spectrometer to analyze more than 8,500 proteins present in fat deposits, helping them detect fasting changes.
Proteomics - the study of all proteins - exposed the inner workings of fat tissue, alerting researchers to significant cellular changes induced by intermittent fasting.
It also emerged that when the body entered fasting, visceral and subcutaneous fat improved its ability to retain energy. Before the next fasting time, the body effectively compensates for the lost fat reserves by quickly restoring them.
"Our data show both visceral and subcutaneous fat undergoes dramatic changes during intermittent fasting," said Dr. Larance.
Why Visceral Fat Could Resist Weight Loss
Fasting allows fat tissue to release fatty acid compounds, which supply energy to the rest of the body.
During fasting, however, the researchers discovered that visceral fat became immune to this fatty acid release.
There were also indications that visceral and subcutaneous fat improved their ability to retain energy as fat, suggesting that the fat reserves were likely to be quickly restored before the next fasting time.
A pattern of prolonged fasting cycles, according to Dr. Larance, may have activated a preservation signaling mechanism in visceral fat.
"This suggests the visceral fat can adapt to repeated fasting bouts and protect its energy store," he said.
This form of adaptation could explain why visceral fat can be immune to weight loss even while dieting for long periods of time.
Dr. Larance suggests that using a mouse model as a guide to human experiments is a smart idea.
He states that the physiology of mice is identical to that of humans. However, since their metabolism is much quicker than that of humans, we can detect changes much faster and analyze tissues that are difficult to sample in humans.
Future studies in mice and humans may expose the pathways behind this resistance, as well as which diets and other treatments are most successful at reducing belly fat.
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