Intermittent fasting diets – for example, the Fast Diet and 5:2 diet – revolve around eating what you want some days a week, and then eating very little on the other days. They have become popular over the past five years. But are they more effective than other weight loss diets? The latest research suggests not.
A study published in an American Medical Association journal in 2017 found that, after a year, weight loss was not significantly different than for daily calorie-restricted diet groups.
Supporters of fasting diets claim they provide health benefits beyond weight loss. Indeed, animal studies have indicated that fasting prolongs life and reduces the risk of diabetes, cancer, heart disease and Alzheimer’s disease. But human studies are scarce and contradictory.
A University of Southern California study of 71 adults published recently found that intermittent fasting reduced blood pressure and risk factors for cardiovascular disease, cancer and diabetes, and reduced body fat too. But another new study, from the University of Illinois, suggests it improves cardiovascular risk no more than any other diet.
What is undoubtedly true is that intermittent fasting diets suit many people because they don’t disrupt lifestyles or family meals too much. “It’s not particularly dangerous because you’re essentially not changing what you’re eating on most days, yet over a week you end up eating less,” says Yeo. “They are very effective for some people.”
Verdict: Intermittent fasting is no more effective than other calorie-restricted diets, but it works for many people as it isn’t too disruptive.
CAN YOU BE FAT AND FIT?
For decades, scientific debate has raged about the role of exercise in weight loss. Today, there is greater scientific consensus that food intake is more important than exercise for losing weight. But the debate goes on about whether being fit mitigates the health risks of being overweight.
Central to the controversy is research from the Cooper Institute for Preventive Medicine in Dallas, which shows that over-60s who exercise have lower mortality regardless of how much body weight they carry. American health psychologist Dr Traci Mann from the University of Minnesota is currently the most prominent figure in asserting that overweight people can live healthy lives as long as they exercise.
She says there is no evidence that overweight people have shorter lifespans, there is just evidence that people who are sedentary, poor and medically neglected (who are also often obese) live shorter lives. “Obesity only really leads to shorter lifespans at the very highest weights,” she says.
There is no point in dieting, she claims. “To reduce your risk for cardiovascular disease and diabetes, you don’t actually have to get thin, you just have to exercise.”
But the ‘fat but fit’ camp has few supporters in the UK, and the theory has received a new setback from a recent study of 3.5 million GP records by the University of Birmingham. This found that ‘healthy’ obese people, who had normal blood pressure and cholesterol levels, were still at higher risk of serious disease than healthy people of normal weight. The obese people had 49 percent increased risk of coronary heart disease, 7 percent increased risk of stroke, and 96 percent increased risk of heart failure.
Verdict: Obese people with healthy blood pressure and cholesterol still have an increased risk of heart problems and strokes.
ARE ANTIBIOTICS MAKING US FAT?
The past five years have seen interest in the idea that our gut bacteria play a crucial role in regulating weight, and killing them off with antibiotics is causing obesity.
The most recent evidence is fascinating but inconclusive. Studies in prestigious medical journals have produced contrasting results. One found that three courses of antibiotics before the age of two was associated with increased risk of early childhood obesity, while the other found that exposure to antibiotics in the first six months of life was not associated with early childhood weight gain.
Yet recent research is indicating a link between gut fauna and our body mass index. People with higher levels of Christensenellaceae bacteria – one in 10 of us – appear less likely to put on weight than those with lower amounts. Scientists from King’s College London have found that levels of this bacteria are partly genetically determined.
According to Yeo, who investigated the possibility of microbial transplants to cure obesity for a BBC programme, this new field is important and requires research. “But I have yet to see convincing evidence that there are lean bacteria and obese bacteria,” he says.
Verdict: More research needs to be done, but our gut bacteria may affect how readily we put on weight.
DO FAT-BURNING TABLETS WORK?
Dozens of ‘metabolism-boosting’ supplements – including ingredients such as caffeine, capsaicin, L-carnitine and green tea extract – claim to stimulate energy processing in the body, increasing the rate at which we burn calories. But there’s little evidence that these products work, and most of their claims are not subject to scientific scrutiny because they are classed as food supplements rather than medicines.
Some studies have indicated that people burn more calories when they take caffeine but, according to the Mayo Clinic, this doesn’t appear to have any significant effect on weight loss. There is little data on most other ‘fat-busting’ pill ingredients, although there is some evidence from small studies that capsaicin, which is found naturally in chillies, can promote loss of abdominal fat and make people feel fuller.
There is a constant stream of news stories about food types that can apparently provide a shortcut to weight loss by boosting metabolism, reducing fat levels or promoting healthy gut bacteria. Cayenne pepper, apples, cider vinegar and cinnamon have all been in the news recently. The problem is that most of these stories are based on small or isolated studies, often in rodents not humans. There may be something in them, but it’s still very early days.
Verdict: There is no easy fix for burning fat. Sorry!
