Why eating less - not exercise - is the key to losing weight
We've become a nation of fitness fanatics, yet studies show that the real key to weight loss is simply eating less. But that message struggles to be heard in a sea of fitness and food marketing.
Published 09/09/2015 | 02:30
Exercise is key to a healthy weight, or so we believe. Fitness has never been more fashionable or ubiquitous. Whether it's Alexander Wang running gear or mass gatherings for weekend yoga in St Stephen's Green, personal fitness is now part of popular discourse in Ireland. A decade ago, work colleagues might have bonded over pints, now they are more likely to go for a run or train for triathlon together.
But is exercise the golden solution it's promoted to be for the 58pc of Irish adults who are obese and simply want to lose excess weight?
TV shows like Ireland's Fittest Family and Operation Transformation that put contestants through punishing exercise regimes are on the right track for quick results. But increasingly, international researchers and writers on obesity are finding problems with the overwhelming emphasis on exercise as a weight-loss tool.
The United States, home of the fitness fad, is beginning to reframe the "exercise is everything" mantra. Aaron E Carroll, professor of paediatrics at Indiana University School of Medicine, recently claimed in the New York Times that, "When it comes to reaching a healthy weight, what you eat is much more important."
Exercise uses up a lot less calories than people think. Running or swimming use up about 350 calories per half hour. But how many times a week can adults reasonably keep up a fairly strenuous exercise regime if they are not fit in the first place and their primary aim is to lose weight?
People who are already in the fitness mindset have no problem running three to five times a week. But if you have two or three stone to lose, running, or even moderate walking, isn't going to solve your problems. It's simply to eat less. A lot less.
Studies tend to confirm this. Carroll cites a meta study (a study of studies), published in Obesity Journal, showing that weight loss resulting from exercise tends to be lower than predicted, particularly as energy balance in the body recalibrates.
"In the adult population, studies have difficulty showing that a physically active person is less likely to gain excess weight than a sedentary person.
"Further, studies of energy balance, and there are many of them, show that total energy expenditure and physical activity levels in developing and industrialised countries are similar, making activity and exercise unlikely to be the cause of differing obesity rates."
Another North American study examined physical activity in kids, concluding that physical activity was not the key determinant in whether a child is at an unhealthy weight.
Gyms don't particularly want people to latch onto this fairly simple idea. Some portray the idea of simply buying membership as the first step on the weight-loss ladder. Exercise excites us. Eating less doesn't. The fitness industry - clothing, equipment, sports drinks, and personal trainers are all pitched as sound, highly motivating solutions as opposed to simply putting less food into your mouth.
Gyms work for many people but have a very high attrition rate for those who still struggle to reduce their calorie intake. So no matter how physically active you are, even at the beginning of a weight-loss regime, if you are not cutting down your food, the overall trajectory is going to be a negative one.
In the fog of nutritional and sham nutritional advice, it might seem easier to try and exercise your way to weight loss rather than cut out foods.
Marion Nestle, professor of nutrition in New York University and one of the world's most respected writers on diet and obesity, comes back again and again to one single point. Don't focus on individual food groups. If you want to lose weight, simply eat less food.
Since the 1970s, we have been fed contradictory and often dangerous advice on eliminating key nutrients from our diet: fats, dairy, carbohydrate and the current enemy du jour - sugar.
The focus on eating or eliminating single nutrients is crucial to how the food industry operates. It is much easier for companies to sell the advantages of one single nutrient or super food in a product than to appraise realistically for the consumer the total effect of ingredients in the product.
"Health claims on food labels distract consumers from their calorie content," says Nestle. "This practice matters because when it comes to obesity, it is the calories that count. Obesity arises when people consume significantly more calories than they expend in physical activity".
The two-decade long war on fats is a good example of how this mania for single nutrient marketing works. In claiming to serve consumers needs, the war on fat was really about food companies worldwide trying to shift "fat-free" products into our trolleys.
This gave rise to 1980s vogue of yellow margarine made from tar like trans fats, and the migration of trans fats into just about anything you could think of - cheese, baked goods, pizzas and, of course, fast food.
The European Commission is now considering banning trans fats from food processing, but why did it take so long to recognise their role in obesity and heart disease? Most consumers in the western world could do with consuming less. But not in one single company manufacturing food worldwide is going to make this point. Eating less food makes money for nobody.
The American Journal of Clinical Nutrition backs up Nestle's views, finding that when it comes to weight loss, how much you eat matters much more than the proportion of fat, carbohydrate, and protein in your foods.
Researchers had volunteers eat diets that were supposed to differ in proportions of fat (40pc vs 20pc), carbohydrates (35pc vs 65pc), and protein (25pc vs 15pc).
The results of the study are consistent with the findings from many previous studies: all the participants who stuck out the diet lost a similar amount of weight. Eliminating more of one particular food group made no difference against an overall cut in calories.
What we know works in the long term is a combination of change in behaviour around food and exercise. Many studies show that a combination of exercise and cutting calories works to reduce weight.
A 2014 study by the Journal of the Academy of Nutrition and Dietetics found that, in the long term, behavioural weight management programmes that combine exercise with diet can lead to more sustained weight loss (three to four pounds) over a year than diet alone.
Over a six-month period, though, adding exercise made no difference. Another meta study found similar results; reducing calorie intake combined with exercise has better weight-loss results than cutting food intake alone, but without much of an absolute difference. So radically changing eating patterns is the long-term key.
Not surprisingly though, Carroll is big on the other benefits of exercise.
"I can't say this enough: exercise has a big upside for health beyond potential weight loss," he says.
"Many studies and reviews detail how physical activity can improve outcomes in musculoskeletal disorders, cardiovascular disease, diabetes, pulmonary diseases, neurological diseases and depression.
"But that huge upside doesn't seem to necessarily apply to weight loss. The data just doesn't support it."
Obesity in numbers
The journal Scientific American just devoted their entire Summer 2015 edition to the science of food and obesity. Here are the figures:
To lose a pound of fat a week you have to reduce your daily intake by 500 calories
An adult expends roughly 100 calories for every mile run or walked briskly. It takes nearly three miles to burn off the calories in an average 600ml soft drink
Alcohol is metabolised in a way that promotes accumulation of fat in the liver. So a beer belly is not just subcutaneous fat but an enlarged liver needing attention
Foods high in fat and sugar prompt the brain's striatum to release endorphins and dopamine - chemicals that regulate our reward systems. In some people, the combination of these chemicals overpower conscious attempts to stop eating when full. So they continue to consume high-calorie foods despite knowledge of health consequences
Over time, these hormones become progressively less effective as the body builds tolerance to their actions and weight increases. MRI imagining of the brain in overweight subjects shows these "muffled reward circuits" depress mood, and the individual tends to eat more to regain the same chemical release
De-regulation of farming and food volumes produced in Europe and the US has promoted the obesity epidemic. We now produce surplus calories to human need (about 4,000 calories a day) so these must be packaged and sold to us in different ways, creating need and desire for extra calories when there is none in reality
In-between-meal snacking, and serving larger portions are ways in which the food industry promoted change in social norms. Nestle says these are inappropriate, unhealthy habits and eliminating them will make a big difference to calorie intake