The Consensus: Intermittent Fasting May Have Health Benefits Outside of Weight Loss
Intermittent fasting is on par to other approaches as a way to lose weight. If there are additional longer-term health benefits outside of those seen with weight loss, science has yet to find a clear answer. This consensus is based on 17 experts answers from this question: Does intermittent fasting have health benefits?
Intermittent fasting may have the appearance that it’s just another short-term diet fad like so many others that have gone before it, but in fact, there is nothing new, novel or faddish about it at all. The first meal of every day, no matter what time it is eaten, is the ‘breaking of the fast’ so you’ve been doing it your entire life. Just to be clear though, fasting is not the same as starvation. Starvation is the involuntary absence of food such as what happens during food scarcity and famine. While fasting is the voluntary withholding of food for spiritual, health, or other reasons.
Tracing back thousands of years, we have the ancient tradition of religious fasting which is common across all the major world religions. The daily sunrise-to-sunset month of fasting of Ramadan is probably the most well-known example of this.
One explanation for the interest in intermittent fasting is the simplicity of it. Fasting bypasses all the debate about what nutrients and foods that should and should not be eaten and instead purely focusses on the length of time between eating. Fasting proponents are mostly agnostic about what foods are eaten during the ‘feasting’ times. A book about fasting is a short read indeed.
How do you fast?
How do you do a fasting diet? There are several different ways - all of which involve splitting the day or week into eating and fasting periods. Intermittent fasting focusses on the time when you don’t eat.
Here are some of the most widely used fasting schedules:
The 16:8 plan involves eating only during an eight-hour period followed by a 16-hour fasting window. So, if you have your last meal at 8 pm at night, you don’t eat again until midday the next day. Rinse and repeat. This method is technically called time-restricted eating (TRE) but falls under the intermittent fasting umbrella
Then there is the elegantly simple Eat-Stop-Eat way of doing fasting. Simply fast for a full 24 hours straight for one or two days per week
Then we have the popular 5:2 diet. This involves choosing two days each week where you will eat only 500 to 600 calories per day but eat normally the other 5 days.
Which method is best? Science is nowhere near answering that question. Many people find the 16:8 method to be the simplest and sustainable method to stick to, but with so many different ways to fast, it offers flexibility for how a person chooses to do it.
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Fasting and weight loss
In looking at the evidence for the benefits of intermittent fasting, let’s start with the big one first: weight loss. There have been enough human weight-loss trials comparing intermittent fasting against traditional calorie restriction to see how they stack up when compared. And that was the topic of a review paper published in the journal Nutrients in October of 2019.
Eleven randomised-controlled trials were looked at and they all ran for at least 8 weeks and involved adults who were overweight. Intermittent fasting was compared to calorie restriction head-to-head in each study. And what did they find? Nothing to get excited about with nine out of the 11 studies finding no difference in the amount of weight or fat lost between the groups
If there is a benefit that fasting offers for weight loss above that other diets give, it is pretty small and not of much clinical significance. The majority of our experts reached a similar conclusion that weight loss isn’t assured for everyone and on average, it doesn’t appear to be superior to other dieting options.
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Other health benefits
Fasting for weight loss is hardly a new idea. But what is novel about the explosion in interest in fasting is the clinical research behind it with claimed benefits for health and longevity. The body of evidence on intermittent fasting in humans is still relatively small, but several studies have reported improvements in various health markers. It is still an active area of debate if there are any unique metabolic benefits to intermittent fasting over traditional chronic caloric restriction.
And once you start talking about benefits outside of weight loss, you’ll soon come up against a term called 'autophagy'. ‘Auto’ means self and ‘phagy’ means eat, so autophagy is the body's way of cleaning out damaged cells literally by ‘eating itself’. This is done as a way for the body regenerate newer, healthier cells. It’s going on inside you right now. But during fasting, cells activate pathways that increase defences against oxidative and metabolic stress and systems that remove or repair damaged molecules. Think of this like a switch that is activated in periods of food scarcity as the body looks for more fuel sources. In our modern times of food abundance and ‘three meals per day with snacks in-between’, it is rare for this metabolic switch to be flipped. But the benefits of the switch have favourable advantages in improving blood sugar regulation, increasing resistance to stress and decreasing inflammation.
So, is intermittent fasting the key to reducing inflammation, cutting the risk of diabetes and heart disease, improving the brain and neural systems and maybe even extending life? A lot of this is really conjecture or based on animal studies at this stage, but a paper published just the last month highly regarded The New England Journal of Medicine has put the health claims about intermittent fasting diets under the microscope.
Weight loss aside, there are some initial indications that intermittent fasting may have some additional metabolic advantages. With animal studies and some human research to inform it, there appears a benefit of fasting on supporting cellular health. Cellular health is a broad term and includes things like the resistance of cells to metabolic and oxidative stress, increased DNA repair and activation of antioxidant defence systems.
Other benefits uncovered by the review included some evidence for intermittent fasting on decreasing blood pressure, blood lipid levels and even resting heart rates. Clinical trials show that even independent of weight loss, intermittent fasting has an additional advantage on insulin sensitivity and abdominal obesity compared to just a traditional calorie-reduced diet.
More speculative, but there appears some preliminary research to show that intermittent fasting could benefit brain health too. One study found that mice that were on a brief intermittent fasting diet had better learning and memory than mice with free access to food. Further research in animals suggests that intermittent fasting can suppress inflammation in the brain, which has links to neurological disease. Other animal studies have found that intermittent fasting can reduce the risk of neurological disorders including Alzheimer's disease, Parkinson's disease, and stroke. One study with 220 healthy adults who maintained a calorie-restricted diet for two years showed signs of improved memory. There is a lot more that needs to be done here.
As for longevity, unless you’re a worm or maybe a lab rat, there isn’t much evidence to show that intermittent fasting will help you live longer. But if it helps with weight loss and reduces the risk of some chronic disease like heart disease and type 2 diabetes, then that is where the benefit could lie.
And finally, for cancer, animal studies suggest that intermittent fasting may prevent cancer, but there is nothing yet to say it will help in humans.
The uncertainty to do with the health benefits of intermittent fasting was raised by several of our experts too. Leanne Harris from the University of Glasgow noted that studies, thus far, have included biomarkers and risk factors for adverse cardiometabolic health conditions including glucose, insulin, and cholesterol levels. There is some evidence demonstrating statistically significant reductions in these outcomes following intermittent fasting. These findings are comparable to dieting every day which is currently recommended by clinical guidelines for weight loss. However, whether reductions in these risk factors reported in these studies are enough to have an improvement in health is uncertain.
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A word of warning
Intermittent fasting isn’t for everyone as Alice Owen from Monash University pointed out. There is insufficient evidence from human studies to be exactly certain how, to what extent, and what the long-term effects might be. There are certain groups of people for whom potential risks may outweigh benefits when it comes to intermittent fasting. These include pregnant and breastfeeding women, those with thyroid dysfunction, people with diabetes and other underlying chronic diseases. People in these groups should consult their medical professional before embarking on any type of dietary change.
There is a ways to go before there is enough evidence to move intermittent fasting into the mainstream as a first-line approach to lose weight and viable way to treat many health conditions. The research so far looks promising, but it does not appear to be a miracle elixir for weight loss and longevity.
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