- Intermittent fasting is one of the buzziest diets out there, with celebrities like Chris Hemsworth and Hugh Jackman claiming that it helped them lose weight
- Some health experts are suggesting that intermittent fasting can improve your immune system, thus making you healthier.
- A 2014 study found that when mice and cancer patients went without eating for four days, their bodies get rid of old blood cells and generated new ones
- But how much truth is behind these claims that intermittent fasting is actually healthy for you?
Hugh Jackman swears it gets him into Wolverine shape. Silicon Valley bros think it enhances mental prowess. And Redditors claim it can help them lose upwards of 40 pounds.
Intermittent fasting, which calls for not eating for anywhere between 16 hours to an entire day, is one of the buzziest diets out there, with many raving that it can help you shed pounds quickly.
But some people are arguing that intermittent fasting has even more benefits: multiplestories have suggested that fasting can boost your immune system, and researchers are beginning to study whether it can improve heart health and lower cancer risk, too.
But are these claims legit? And for that matter, should you even try intermittent fasting in the first place?
Let's get one thing straight right off the bat: There's not enough research to say for sure whether fasting has any health benefits, says Liz Weinandy, M.P.H., R.D., a staff dietitian at the Ohio State University Wexner Medical Center.
“I don’t think anybody knows,” says Weinandy. “This is all preliminary.”
In fact, most of the press coverage of intermittent fasting and its purported immune system benefits has focused on just one study.
In 2014, biochemist Valter Longo, the head of the anti-aging department at USC, had both mice and human cancer patients fast for four days. During the fast, both the mice and the cancer patients discarded old blood cells; once the fast was broken, their bodies produced shiny, new cells to take the place of discarded ones, thus effectively regenerating their immune systems.
The results of Longo's study led him to conclude that prolonged periods of fasting could reduce the harsh side effects of chemotherapy for cancer patients (in fact, some patients are already trying this on their own), or even boost immunity for healthy people.
A 2015 study from Yale Medical School went one further, finding that both dieting and fasting produce a compound that prevents the immune system from making a protein linked to inflammatory diseases like diabetes and atherosclerosis. That study also assessed both human and mice immune cells.
OK, but does intermittent fasting actually make you healthier?
While Longo's study might sound promising, it's important to note that the data was collected from animals and a small group of cancer patients, so it does not reflect a larger, more diverse sample of human subjects.
Further, most intermittent fasting plans recommend not eating between 16 to 24 hours — a much shorter period of time than the four-day fast in Longo's study. For this reason, Longo says it's unlikely that his study has any long-term implications about the health benefits of intermittent fasting.
Your body won't eliminate old cells "until two, three or four days into the fasting," he says. "It takes even longer for the system to start really breaking down muscle, breaking down immune cells, breaking down different tissues."
Weinandy also points out that future studies will require a broader sample size than Longo's, so we can determine how fasting affects different groups of people — for instance, the elderly, or diabetes patients.
"There’s going to have to be a ton more research" for us to know if fasting has any long-term health benefits, she says.
So we know that intermittent fasting is not necessarily good for you. Is it even safe to begin with?
The overall consensus is that for healthy people, intermittent fasting is relatively safe and about as effective as an extremely low-carb diet in terms of encouraging weight loss.
There are, however, a few exceptions: if you have a compromised immune system or impaired liver or kidney function, you probably shouldn't fast. If you have an active lifestyle, Weinandy also cautions against exercising while fasting for a full day. She says it could potentially drain sodium and potassium stores in the body, two important electrolytes that are essential for kidney, heart and muscle function. Nausea, weakness, and muscle cramps are all signs of low electrolytes and could indicate you have a problem. Drastically cutting calories while exercising could also lower your overall metabolism.
Perhaps surprisingly, Longo also doesn't recommend fasting for more than 12 hours. Instead, he's devised a five-day diet plan including soups, crackers, and tea, which he says is designed to trick your body into thinking it's fasting so it can reap the benefits. The product debuted at $300, and now costs $249 (it drops to $225 if you commit to three boxes).
But Weinandy says there's no need to abstain from eating or buy special food to mimic fasting. She says that a balanced diet is hands-down the best way to maintain overall health.
And when it comes to the overall hype about fasting in general, she advises people to be skeptical. “You really have to look at things like this very cautiously,” she says.
(Still want to learn more? Check out The Men's Health Guide to Intermittent Fasting)
Melissa MatthewsHealth WriterMelissa Matthews is the Health Writer at Men's Health, covering the latest in food, nutrition, and health.
"You really have to look at things like this very cautiously."
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