When people want to lose weight, the potential benefits of fasting can seem very appealing because only eating for a certain period means you potentially consume fewer calories.
But what is fasting? According to a nutritionist Marcello Fiuza (opens in a new tab)press secretary British Dietetic Association (opens in a new tab), fasting means not consuming calories for a period of time. It can be “intermittent,” which means you alternate between eating and fasting, or “continuous,” which usually means fasting for two days or more.
“Intermittent fastingin particular, with a time limit, e.g 5:2 or 16:8, has become popular in recent years,” she adds. “This involves eating within a limited time window each day, usually between eight and ten hours.”
In addition to weight loss, many people fast solely for the potential benefits, including improved gut and heart health and lower blood pressure. But it is important to note that fasting does not guarantee such results, and it is not suitable for everyone – especially people with eating disorders, pregnant women, diabetics, the elderly and children.
In this article, we talk to Fiuza about the possible benefits of fasting, as well as some of the downsides.
What does fasting do to the body?
Before we look at the possible benefits of fasting, it’s important to know what it actually does to the body.
Fiusa explains, “During fasting, the body makes a number of metabolic adaptations to maintain optimal functioning in the absence of external fuel (food). During the first few hours of fasting, the body turns to glycogen stores for energy. When these are depleted, a metabolic switch occurs in which the body begins to break down fatty acids into ketones which are then used as a source of energy.
Marcelo Fiusa is an award-winning registered dietitian based in London, UK. She has ten years of experience in the National Health Service, private practice and the commercial sector. She has a Masters in Nutrition and a Postgraduate Diploma in Dietetics from King’s College London. She is a member and spokesperson for the British Dietetic Association.
“The time for this metabolic switch depends on what your last meal was, how much energy you consume and how much glycogen is stored in your liver. On average, it can be 12-26 hours without food.”
Of course, not all benefits are guaranteed. “A lot of research, mostly in animal models, suggests the benefits of fasting, and there’s more and more evidence coming out of human trials,” Fiusa says.
“But more research is needed until we can fully understand the long-term effects of fasting on human health.”
1. Autophagy
One possible benefit of fasting is that it can trigger a process called autophagy, your body’s cell recycling system. Acting as a kind of quality control for your cells, autophagy allows the body to break down and reuse old parts of cells so they can work more efficiently.
Simply put, according to a study conducted by Embo magazine (opens in a new tab).
The process of autophagy begins after a period of starvation and may be an evolutionary throwback to our hunter-gatherer days, when humans went longer without eating due to the laboriousness of finding food.
Researchers are studying the role of autophagy in the potential prevention and control of disease, Fiusa says. “Evidence from a study published in Science Direct (opens in a new tab) suggests that fasting may enhance autophagy.’ Another study published in Journal of Autophagy (opens in a new tab)showed that regular fasting can “reset” the body and help it work more efficiently by clearing cellular debris.
2. Improving gut health
This evidence (opens in a new tab) suggest that a radical change in diet, such as fasting, can change the microbial composition of the gut and change what the gut bacteria do.
Fiusa told Live Science, “Some forms of fasting may be beneficial for the gut microbiome, which is associated with a number of health benefits from improving metabolism, reducing the risk of cancer, heart disease and obesity.”
Other studies have shown that alternate fasting (24 hours of eating, usually after 24 hours of fasting) promoted “bacterial cleansing” that could support a healthy gut microbiome.
3. Healthy heart and blood sugar
Fasting can also improve the body’s response to the hormone insulin, which controls blood sugar levels. When blood sugar levels are regulated, it reduces the risk of weight gain and diabetes, which are two risk factors for cardiovascular disease and other heart-related health problems.
Fiusa adds that intermittent fasting can also improve heart health by lowering low-density lipoprotein (LDL), or bad cholesterol, as well as “having positive effects on blood pressure regulation and reducing inflammation,” but more research is needed in this area.
4. Weight loss
Fasting has become increasingly popular as many people see it as a way to lose weight. “It could potentially help some people lose weight in the short term,” Fiusa admits. “Although it does not appear to be superior to other types of calorie-restricted diets for this purpose.” And ultimately, to lose weight, you need to be in calorie deficit.
A systematic review in a peer-reviewed journal Canadian Family Physician (opens in a new tab) found that in all 27 trials reviewed, intermittent fasting resulted in weight loss ranging from 0.8% to 13.0% of baseline body weight.
But as with all extreme eating plans, there are some downsides to consider, Fiusa says.
“There are potential side effects of fasting, but most of them go away over time. The main ones are lethargy, irritability and headaches, but there is also the risk of disordered eating for those prone to eating disorders.
“Intermittent fasting is much more intense than intermittent fasting, and anyone considering it should talk to their healthcare provider beforehand. Intermittent fasting may not work for everyone either.
“People who are pregnant or have type 1 diabetes, who have eating disorders or take medication with meals, as well as children and the elderly should avoid fasting.”
If the post seems unappealing to you, check out our guide to Mediterranean diet instead.
This article is for informational purposes only and is not intended to provide medical advice.
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