Dr. Christopher Labos is a Montreal physician and science communicator. He is co-host of the Body of Evidence podcast and a regular contributor to Montreal Gazette. Dr. Labos writes about what reproducible evidence has to say on important scientific and medical concepts. You can follow him on Twitter @drlabos .
The other day, over dinner, I got into a debate with some friends about intermittent fasting. It’s a new diet strategy where you eat restrictively on some days but then eat freely, almost indulgently, on others. Although many forms of intermittent fasting exist, the most common form I’ve seen is what’s called alternate day fasting.
With alternate day fasting, you can eat very little on one day (usually one 500 calorie meal at lunch time, or about one-quarter of what a regular diet includes) and then essentially eat to your heart’s content on the next day before repeating the two-day cycle.
The idea has an obvious appeal. Dieting is hard because eventually, people find the restrictive nature of most diets impossible to stick with and revert to their old ways. But alternate day fasting seems easier because most people can summon enough willpower for one day if they know they can be libertines tomorrow.
The obvious question becomes, does intermittent fasting work? Will it help you lose weight? And perhaps most important, does it outperform a standard diet where you just eat a little bit less every day?
That question was answered recently in a study published in JAMA Internal Medicine. Researchers took 100 obese adults and divided them into three groups. The first group was told to continue their regular habits. The second intermittent fasting group ate a single 500-calorie meal on “fasting” days while on “feasting” days they could eat up to 25 percent more than they usually did. The third group was told to follow a conventional diet where they simply ate less every day.
The results were a surprise to the researchers. There was no difference between intermittent fasting and conventional diets. Both groups did equally well. Or if you are a nihilist, both groups did equally badly. At six months, both groups had lost just under seven pounds. By one year, the number had slipped back to about six pounds.
These numbers probably don’t seem that impressive. On TV, you can drop 30 pounds in a few weeks. In real life and clinical trials, 5-10 pounds over the course of a year is more realistic and actually quite impressive.
But intermittent fasting proved to be a disappointment in this trial. It did not outperform its conventional counterpart. In terms of weight loss, visceral fat, blood pressure, blood sugar, insulin levels and inflammatory markers, there was no difference between intermittent fast and simply eating a little less on a daily basis. In fact the intermittent fasting group had slightly higher cholesterol levels at one year, although the difference was minimal.
Here, intermittent fasting underperformed because rather than being easier to stick with, it ended up being harder. More people abandoned the intermittent fast (38 per cent vs. 29 per cent) and ended up switching to conventional diets.
In the end, intermittent fasting is not better than a standard diet. It won’t help you lose more weight and it won’t make you any healthier. Though to be fair, it’s not much worse, either. And contrary to the hype, it actually seems to be harder to stick with long term, not easier.
I’m sure some people will swear by intermittent fasting and say that it works for them. The point here though is not that one diet is better than other. It’s that diets work only if they get you to eat less. Eating less is really the only way you can lose weight (although regular exercise certainly won’t hurt). How you do it isn’t really as important as whether you do it. Fad diets fail because they are unsustainable and people abandon them. So when I’m asked what’s the best type of diet, the answer is clear. The best diet is the one you can stick with.
This article was originally published in the Montreal Gazette.