In the US, intermittent fasting (IF) was the most popular diet of 2020 nudging ‘clean eating’ from the title and just managing to fend off keto. Time-restricted eating—the research name for intermittent fasting—is immensely popular worldwide because it’s easy to follow, and there are loads of research. Benefits of the diet include cancer-fighting, improved immune function, better cognition, and fat loss.
I practice the 16:8 version, use it to great effect with clients and have written about it. But, recent research may have thrown a spanner into the works. Read on to discover if it’s time to bring breakfast back to life.
The Spanner
The troublesome research, published in the Journal of the American Medical Association (JAMA). I set out to discover ‘the effect of time-restricted eating on weight loss and metabolic health in patients with overweight and obesity.’. It’s a decent-sized randomised control trial, with 116 humans split into groups for the 12-week duration.
The most interesting group is the time-restricted eating (TRE) group who were instructed to eat only in an 8-hour window each day. For comparison, the scientists conducting the trial asked a control group to eat three meals per day, plus snacks when they desired. They received no other dietary tidbits.
Both groups lost weight during the study; a phenomenon that often occurs when enrolled in a weight-loss trial. At first glance, the TRE group results tallied with the bias of the lead scientist, Dr Weiss, a man who diligently applies IF to his daily routine.
The fasters had lost an average of 1.17 kg (2.6 lbs), but the control group wasn’t far behind with a mean loss of 0.75 kg (1.65 lbs). These results are nothing to write home about; I’d expect to see the higher number after a week. But, there was a more serious problem; nearly half the weight lost amongst the fasters was muscle mass. The loss of muscle mass while dieting is not a desired outcome. Muscles are engines that burn up calories every day. Reducing the size of your engine means more calories are stored as fat. Ensuring your muscles stick around is protective of metabolic diseases and non-alcoholic fatty liver disease.
Muscle mass, within reason, is consistently associated with longevity amongst older adults. Skeletal muscles act as buffers against frailty, protecting the elderly from common injuries like a broken hip. Fat doesn’t offer the same protection but exchanges pros for cons.
The researchers concluded that ‘time-restricted eating did not confer weight loss or cardio metabolic benefits in this study.’.
It may just be that people consume fewer calories when they restrict their eating window, and that’s fine for many as long as nutrients, including protein, are kept at sufficient levels.
Before you crack open the Kelloggs
Any diet that sees a large percentage drop in muscle mass is one to avoid. But, before you crack open the Kelloggs, let’s take a closer look at what may be happening. Remember, the people enrolled in the trial were not given any advice about how much protein, fat, or carbohydrates to eat.
The one of importance here is protein. The researchers did not measure differences in protein intake between the groups. Nor did they assess the total amount in the TRE group. This is critical because protein builds muscles, and is required daily to stop the body from breaking the existing muscles down.
A randomised control trial, set over eight weeks, tested intermittent fasting (with a 4-hour eating window) against a typical eating pattern. Besides, the young men performed a very run-of-the-mill resistance training programme three times per week. The fasters consumed ~650 fewer calories per fast-day and enjoyed increased muscle mass and strength that exceeded the control groups. What was their secret?
It is a larger percentage of energy from protein and a smaller amount from carbohydrates versus the control group. Interestingly, the fasting group consumed less total protein per lb of bodyweight than the normal eaters. This highlights the need for appropriate amounts of protein, not total amounts, particularly when working out. It also casts doubt that intermittent fasting is damaging to muscle mass for any other reason than eliminating an entire meal from your day may result in lower total amounts of protein. I think this is the real problem with the JAMA study.
Will I change the way I practise?
I pride myself in changing my opinion when new evidence arises, but a single study with a gaping flaw will not alter my course on intermittent fasting just yet. I’ll keep recommending it to clients because it’s simple and effective.
It may just be that people consume fewer calories when they restrict their eating window, and that’s fine for many as long as nutrients, including protein, are kept at sufficient levels. Another benefit to skipping breakfast—the most common way of adopting IF—is that those horrible junk foods, sadly, synonymous with breakfast are dropped from people’s diets. Sugary cereals, marketed by a cartoon are an insult to nourishing foods and should be consigned to the naughty shelf. When people start their day with this kind of junk, they open themselves up to lots of energy, few nutrients, cravings, weight gain, metabolic dysfunction and disease. It’s that simple.
The bottom line
The important thing to remember here is this; when people lose weight (fat), their health improves. The JAMA study set out to show a reduction in weight and cardio metabolic markers. They didn’t see the former, and so missed out on the latter.
Reducing muscle mass is not helpful. No diet is magic; every diet should include enough nutrients, macro and micro, to perform at your best. Ironically, this may be achieved by quitting a meal all together. The mechanisms of IF are not completely clear, it may be that people alter their eating behaviours as I have alluded to above, or the absence of food may also be helpful for short periods of time. What is certain is that fat loss improves health across a wide array of markers.
Stick to real foods, don’t let snacking undermine your meals, and never change healthy behaviours based on a single study. If intermittent fasting is working for you, because you fill your feeding window with healthy foods, don’t stop just yet.