Intermittent fasting is an increasingly popular way to attempt to lose weight by forgoing meals. A new review concludes diet restriction might not be enough to shed some body fat, at least not on its own.
Researchers from the University of Southern Denmark, and Wageningen University in the Netherlands, have summarized the existing knowledge we have about the practice of fasting.
A lot of data has been collected over the years, covering multiple aspects of the way that intermittent fasting affects the body. One of the key takeaways is that intermittent fasting has to be combined with managing the intake of calories in order for any weight loss to be seen. It’s the reduction in total calories that makes the difference, rather than long breaks between meals.
“When you do intermittent fasting, the fundamental rule still applies that we should consume fewer calories than we burn, if we want to lose weight,” says molecular biologist Philip Ruppert from the University of Southern Denmark.
“This means that intermittent fasting does not give you a free pass for eating unlimited quantities of food. It’s basic physiology, and fasting can’t change that.”
There’s a lot of ground covered in the review, looking at the effects that intermittent fasting has at the molecular level. These include the release of the breakdown of the body’s store of fatty acids to provide energy, and ketogenesis (when high rates of this fatty acid breakdown leads to the liver producing ketones).
The paper also touches on the feelings of euphoria that some people get after several days of fasting, as feelings of elation start to replace feelings of hunger – perhaps in response to the changing chemical processes going on in the body and the brain.
This is something Ruppert himself has experienced while fasting. For now, scientists aren’t sure why this happens, but one possibility is that ketones are supplying energy more efficiently to the brain, so it hums along in a happier state.
“The brain is fed with ketones during fasting,” says Ruppert. “Maybe that’s why you may experience this clarity.”
There are various different approaches to intermittent fasting, with some people not eating for certain hours in the day, and others not eating during certain days in the week. Plenty of well-known public figures have signed up for these diets too.
And the research team points to numerous health benefits of fasting beyond weight loss that have been recorded, including lower blood pressure. What’s clear though is that everyone is different in their response to fasting, and it’s important to consult with a doctor if you’re thinking about lowering your food intake.
“There are indeed many health benefits to intermittent fasting, but fasting itself does not lead to significant weight loss,” says Ruppert.
The research has been published in Trends in Endocrinology and Metabolism.