If you're intrigued by the 5:2 diet or other forms of intermittent fasting, you probably want to know if these diets work in the long term. Until recently, we didn't have much data. Now, we have a little bit: Fasting every other day turns out to deliver the same results as regular dieting.
Last Tuesday, I ate some green beans, a Clif bar, and one homemade sous vide egg bite. That's 2000kj. I swear I don't have an eating disorder — it's just how you do things on this diet I've been trying. On Wednesday I was back to my regular 8400-ish kj and feeling fine.
The study, published in JAMA Internal Medicine, followed people through six months of trying to lose weight and six months of a maintenance diet. During the first six months, one third of the 100 subjects could eat whatever they wanted; one third had three meals a day provided, making up 75 per cent of their kilojoule needs (so, 6276kJ a day if they would normally eat 8368kJ); and the fasting group alternated between a 25 per cent (2092kJ) day and a 125 per cent (10,460kJ) day.
By the end, both groups kept off the same amount of weight (just five to six per cent, which is 4.5-5.5kg for a 90kg person) and had similar numbers for blood pressure, heart rate, cholesterol, insulin resistance and fasting glucose.
The biggest difference between groups? The dropout rate. The fasting group lost 13 out of 34 people (38 per cent), with five of those saying they were quitting because they hated the diet. The group on the steady diet only saw 29 per cent of their members leave, and none of those cited the diet as the reason. The control group lost 26 per cent of people. Remember, these folks all had to keep in touch with the researchers for a year, and the dropout numbers include people who just plain flaked out. The averages above, like the 4.5-5.5kg lost, include the people who dropped out. So that means weight loss may have worked a little better for the intermittent fasters who stuck with it.
The diets ended up being more similar than intended. People ended up eating more than just the provided food, and they ate too much on fast days and too little on feast days. That's another way in which this diet was hard for people to stick to.
So does this study prove intermittent fasting is nothing special? Yes and no. The subjects were "metabolically healthy" obese women, while proponents of IF often say its value is in fixing a broken metabolism. And the food they ate was pretty standard, carb-heavy fare: Fifty five per cent carbs, 30 per cent fat, 15 per cent protein. Many intermittent fasters combine the regimen with lower carb food, relying on protein, fat and fibre to provide most of their kilojoules.
Finally, it's just one type of fasting. The 5:2 diet gives you a little more time between fasts. Another common way to fast is to go 18 hours of each day without eating: Basically, skip breakfast and eat nothing between yesterday's dinner and today's lunch. We don't know if these other formats would be better or worse than alternate-day fasting, but you can always try them and see.
Bottom line, intermittent fasting isn't good enough to blow traditional dieting out of the water. But it's worth a try, if you think it might work for you.