Bad(ish) News for Intermittent Fasting

In this week's Rundown, intermittent fasting gets a reality check, high intensity exercise may keep you from craving fatty foods, and you can run fast without swinging your arms.

The Rundown

Bad(ish) News for Intermittent Fasting. In a study (read the abstract) sure to upset fasting dieters everywhere, researchers found that a specific type of time-restricted fasting, known as the 16:8 diet, which limits all food intake to an eight-hour period every day, is not more effective as a diet strategy than counting calories.

The trial involved 139 subjects who were either overweight or obese but otherwise healthy. One group did the 16:8 diet, while the other ate at any time. Both groups had to limit their daily intake of calories, with men restricted to no more than 1,800 calories and women to no more than 1,500 calories. This calorie restriction allowed the researchers to focus on the particular weight loss or metabolic outcomes of time-restricted eating. The trial lasted a year.

The participants in the time-restricted eating group lost 9 percent of their body weight compared to a 7.2 percent loss in the all-day eating group. Noting that the difference is not statistically significant, the researchers concluded that calorie restriction rather than time-restricted eating drives weight loss. Similar effects were found when they looked at reductions in body fat, visceral fat, blood pressure, glucose levels and lipid levels over the 12 month trial.

Some things to note: The study is not saying that every type of intermittent fasting is useless. The strategy may have benefits for people with pre-existing metabolic or cardiovascular problems and it may help those with habitual eating patterns. Fans of time-restricted eating suggest that it’s easy to maintain over a long period of time and this study had high retention rates in both groups. But, the participants were closely monitored and coached throughout the year.

The takeaway is that for some people, following a 16:8 plan in order to lose weight may be easier than counting calories but limiting calories is still the key. Eating anything you want for eight hours a day and then fasting for 16 will not take the weight off.

Just Say No: Exercise Edition. A new study (read the abstract) suggests that high intensity exercise may help lessen cravings for fatty foods. Published in the journal, Obesity, the research focused on “incubation of craving,” which refers to the theory that the longer we are denied something, the more we crave it.

To examine if exercise can help us ignore cues that lead to unhealthy eating, the researchers trained rats to seek out high-fat food pellets by pressing a lever that turned on a light and made a tone to act as a cue before dispensing the pellets.

The rats were then placed on a 30-day diet with no access to the pellets and divided into two groups. One group was made to perform high intensity treadmill running and the other was left to their regular activity. At the end of the diet period, the rats were given access to the pellet lever but this time, pressing it only turned on the light and sounded the tone.

The non-exercise group of rats pressed the lever significantly more times than the group that exercised. While the results suggest that high intensity activity suppressed the rats’ cravings for high-fat food, the team notes that the research is still in its early stages. Next steps are to look at the effects of different types of exercise on “incubation of craving” and the mechanisms at work in the human brain.

Awkward Runners, Rejoice. In athletics, arm drills are commonly used to improve running performance. The idea is that sprint speed relies on how much force you can deliver into the ground and swinging your arms helps to put your body in a better position to drive your foot down. A team of researchers decided to test this theory by asking: How fast can you sprint without using your arms?

In the study (read the abstract) published in the journal, Gait & Posture, seven track athletes and ten team-sport athletes (mostly soccer players) performed six all-out 30 meter sprints, three with normal arm movement and three with their arms crossed across their chest. The team-sport athletes started from a standing position. The track athletes started from blocks, with the researchers setting up raised platforms on either side of the blocks so the athletes could start balanced on their elbows.

The normal sprint was faster for both groups but what is surprising is that the difference was only 1.6 percent. The track athletes averaged 4.55 seconds using their arms and 4.63 without, while the team-sport athletes averaged 5.01 and 5.08 seconds, respectively.

The researchers don’t dismiss the usefulness of arm work, saying it may provide “indirect benefits,” particularly in younger and developing athletes. But considering that no arm swing slows your sprint speed a mere 1.6 percent, a “perfect” swing is seemingly overrated.

Replay

This week’s vintage moment in fitness culture is brought to you by kitchen calisthenics, circa 1982, where participants shook salad dressing, among other things. Photo credit: Sara Krulwich/The New York Times.