Some of these days' weight loss articles are bordering on the insane. New scientific studies that shed light on how metabolism works are wonderful and valuable in and of themselves, but something is wrong when the findings are transformed into magical new "tips" for losing weight. Some recent articles in prestigious journals, which sought to dispel weight-loss myths and individual diet myths, suggest that the medical community, too, is tired of the hype and unfounded assumptions that pervade public discourse.

When it comes down to it, the truths we know about weight loss are simple and few. When carried out, they're also extremely effective. So, based on the findings of decades of research, here's pretty much everything we know about weight loss today, condensed into six points about how the body gains, loses, and maintains its weight.

1. Exercising takes a back seat to dieting.

We often hear that getting a little exercise is the key to losing weight – that, for example, taking the stairs rather than the elevator will help. According to Samuel Klein, MD, of Washington University School of Medicine, cutting calories is much more efficient. “It is far more effective to lose weight by reducing food intake rather than increasing physical activity. You can either run 3 miles in the park or avoid eating 2 ounces of potato chips to achieve a 300 calorie energy deficit.” It's that simple. Some studies have confirmed this dichotomy, pitting exercise against diet and discovering that dieting alone results in greater weight loss than exercise alone. Of course, combining the two would be ideal.

The problem is that relying solely on exercise can backfire for a variety of reasons. This is partly due to the effects of exercise on hunger and appetite hormones, which make you feel hungrier afterward. “If you walk briskly for an hour and burn 400 calories, and then have a beer and a slice of pizza because the exercise made you hungry,” says Klein, “you will eat more calories than you burned.” It may not always be beer and pizza, but people do have a natural tendency to compensate for the calories they burn.

David Allison, PhD, adds, "This is an adaptive system." “There is a reaction for every action; that is a physics law, not a biology law, but it appears to work in biological systems as well. This is why we frequently overestimate the effect of a particular treatment.” He goes on to say that public health campaigns encouraging people to take the stairs instead of the elevator or go for a nightly stroll – or, for that matter, eat fewer calories – are unlikely to succeed because they may fail to account for the body's compensatory mechanisms, which can completely counteract the effects of the treatment.

The other issue with exercise-without-dieting is that it is exhausting, and the body will compensate once again. “You might not experience any net negative energy if the exercise made you tired and you became more sedentary the rest of the day,” Klein says. Some of the calories we burn throughout the day come from our basic movements, so if you're exhausted after a jog and more likely to sit on the couch, you've lost the energy deficit you gained from your jog.

2. Exercise can assist in the repair of a “broken” metabolism, particularly during maintenance.

“People used to come into my office and say, ‘My metabolism is broken!'” says James Hill, PhD, of the University of Colorado. “Until recently, we didn't have any proof that it was true. We were completely wrong – it was!” While exercise may not be as important for weight loss as calorie restriction, it is crucial in another way: it helps to repair a broken metabolism, according to Hill.

He claims that “a lot of what we know in this area comes from NASA, from bed-rest studies.” “After just a few days of inactivity, the metabolism becomes rigid. You begin to move again, and things begin to change.” Your metabolism may never return to “normal” (more on that later), but evidence suggests that it can be reactivated, in part by moving your body every day.

This is why exercise is so important during the maintenance phase, which is known to be more difficult than the weight-loss phase. According to Michael Jensen, MD, of the Mayo Clinic, "it basically buys us some wiggle room." “Exercise is critical for weight loss maintenance, and people who are not physically active are more likely to gain weight. We think it's partly because you have a little more flexibility in food intake because of the extra calories burned from physical activity, so you're not as reliant on ridged changes in eating habits; it makes it more tolerable.”

3. You'll have to work harder than other people for the rest of your life – possibly forever.

Though exercise can help a metabolism that has been out of whack for a long time to get back on track, the grim reality is that it may never be the same as it was before you gained weight. So, if you've been overweight or obese and lose weight, you'll probably have to work harder than other people to maintain your weight loss, possibly for the rest of your life. “The sad thing is that once you've been obese or not moving for a while, maintaining your weight requires a little more exercise,” Hill says. It will not return to normal.” It's not a pleasant reality to face, but it's necessary to do so .He says this so you won't be disappointed when you realise you'll have to put in more effort in the long run than your friend who has never been overweight.

Building muscle can help you burn a few extra calories throughout the day, but you'll also have to work harder aerobically in the long run. Hill continues, "It's not fair, but that's the way it is." “However, once you understand it, you know it and it is better. Because you're capable of working with it.”

4. There is no such thing as a magical food combination.

We often believe that if we just figure out the "right" food combination, we'll magically lose weight or keep it  all available. Jensen points out that there doesn't appear to be any "right" diet, and there's no evidence that one diet will work better with a given person's metabolism. “There is a huge myth out there,” he claims. “Is that there is a magical combination of foods – be it protein, vegetarian, or whatever – that will be unique due to its unique interaction with your metabolism? We all know that following any diet will help you lose weight if you stick to it. There is no such thing as a miracle diet. The truth is that if you stick to any diet, it will work.

5. A calorie is a calorie



And when it comes to energy balance, it's all about the calories. This idea is demonstrated by weight reduction on the Twinkie Diet: Mark Haub of Kansas State University dropped 27 pounds by consuming junk food last year. And, according to Yale University's David Katz, MD, who has written extensively on the futility of the "is a calorie a calorie?" dispute, this is a very strong proof of concept.

It's true that all calories are created equal — at least in principle and occasionally in practise. “A calorie is a calorie no matter where it comes from in terms of body weight,” says Marion Nestle, PhD, of NYU. You may acquire weight by eating both nutritious and harmful foods in excess. It's best to consume your vegetables for health reasons.... It's simply easier to consume too many calories from junk food than from nutritious foods. But it is possible.”

However, the source of calories is important for other reasons. One is that "calorie quality is a key predictor of the quantity we eat under real-world settings," according to Katz. First and foremost, no one overeats vegetables, therefore this is a non-issue. “However, where the calories originate from does matter in that they impact satiety,” he says, noting that this is a combination of psychology and biology. In fact, the food industry has developed a new field of food science to research the "bliss point," in which meals are designed to increase the length of time it takes to feel satisfied and full. “We have the 'bliss point' research to inform us that the food business can process meals to increase the calories required to achieve satisfaction,” Katz adds. We have a substantial body of work, including the Harvard ONQI research, that shows that more nutritious' entails, among other things, the ability to eat more food while burning less calories.

True, the foods you consume might change your metabolic profile over time, so they may play a role in this, but when it comes down to it, sticking to any low-calorie diet will generate the energy deficit needed to lose weight. So the point isn't to debate what a calorie is, but rather to recognise that we need to "trade up" our foods, according to Katz, by swapping out calorie-dense foods for foods that are less calorie-dense but more nutritionally dense, such as those that are bulkier, less energetically dense, have more or higher quality protein, have a lower glycemic index, and are more fibrous.

6. It's all about brain



When it comes down to it, it's the brain, not the body or the metabolism, that causes overweight or obesity, as my colleagues have reported (here and here). We all intuitively understand that poor decisions lead to weight increase, whereas better decisions lead to weight loss. The issue is that bad decisions over time cause major changes in how the brain regulates – and, astonishingly, responds to – hunger and satiation processes. Years of any sort of behavioural habit, even overeating, leave brain traces.

The good news is that there's mounting evidence that the brain can "repair" itself in large part once new behaviour patterns arise (i.e., calorie restriction, healthy food choices, and exercise). While there may be some "injury" to the brain, notably in the way hunger and satiety hormones operate, the brain can self-correct to a considerable extent over time. The important thing to remember is that the process takes time and, like any other habit change, requires practise. “We want to alter the culture here,” Hill adds. “Anyone who claims it will happen in 12 weeks is lying to you. We're attempting to reprogram the human brain. Neurobiology has revealed a great deal about what causes weight growth and reduction. Developing new habits, rituals, and routines takes time. This might take months or even years. But it will take place.”

So, to summarise: cut calories, eat healthier, exercise, and most importantly, remember that this is a habit that must be maintained over time – months or years. It's disheartening to realise that you'll have to work more at maintaining your weight than your never-overweight best buddy, but it's something worth accepting. And, most importantly, keep in mind that your brain (after all, the organ at the centre of it all) is malleable, and it will adapt to your adjustments better than you imagine. Your body will as well.