Every popular diet has a theory about why it works, but what diets actually do work? Dr. Kory Gill, an assistant professor and Director of Sports Medicine at the Texas A&M Health Science Center College of Medicine’s Family Medicine Residency program, a team doctor for Texas A&M Athletics, and a member of the Texas A&M Physicians group, has been looking at this question for a while now. We sat down with him to see how far he’d go in repudiating popular fad diets, what the data actually says, and what all workable weight loss strategies have in common.

Q: What’s a fad diet? How do I know if I’m being swept up in a fad, as opposed to following a dieting strategy that will work?

A: Fad diets are diets that are on the market and then off the market. They appear out of nowhere, they generate a lot of buzz, a lot of people try them, and then they fade and go away. They promise quick, dramatic results, and are not focused on long-term solutions. In the short-term, they generate positive buzz, because intensely following any dieting regimen is likely to help someone lose weight in the short-term. But they also impose a burden on people that can’t be maintained over the long-term, and people gain the weight back.

These diets aren’t really even intended to be long-term solutions, although many people begin them hoping for a long-term solution. So fad diets tend to create unrealistic expectations for people. In general, I would characterize a “fad diet” as any diet that has as its major selling point restricting your access to particular foods, or designing a certain regimen of things you must consume, which means the diet is difficult to maintain for a long time. The testimonials are collected while people are on the diet, but there’s rarely a follow-up ad showcasing the people who lost weight and then gained it back.

All diets can be reduced to one basic fact: If they decrease your calories, you’re going to lose weight. Diets that decrease calories more aggressively also make you lose weight more aggressively. Things like the liquid diets are easily able to modify your calorie intake to a daily calorie intake of 500 or so, which is extreme. But can you maintain a 500-calorie a day diet for the rest of your life? Absolutely not. It is not healthy and you cannot maintain it because you are going to burn out. Once you do, the weight doesn’t stay off – it comes back.

Q: So regardless of what food the diet is restricting, whether it is carbs, gluten, or anything processed, those are just masks for what the diet is really doing, which is just reducing calories.

A: Basically, yes. There is more to diets than weight loss, because there are other factors such as the diet affecting your cholesterol and other health factors. But in regards to weight loss, it’s strictly about calories in or calories out. To lose weight, you either take in fewer calories, or you burn the calories that you took in so that your final calorie balance is low.

Q: It sounds like you are saying all of the diet innovations since doctors nailed down the calorie thing have been smoke and mirrors.

A: To some degree, yes. People have various non-weight loss benefits that they propose as the benefits of using their system – reducing your appetite to make it easier for you to eat the low-calorie diet, or making certain foods easy to fit into your lifestyle. For example, “You don’t have to plan out your meal for the day; you just have to take this shake along with you.” So they’re trying to simplify your process of taking in fewer calories. Fad diets work differently in terms of what they do in your body, and how they work in the short-term, if they do at all. But long term, those diets are hard to maintain. Although they are simple, we as humans like variety and we do not thrive on living off a low-calorie shake for the rest of our lives.

Q: But surely not all calories are created equal. Some things are more filling than others – is that purely a factor of how many calories it has? Or could a diet that is restricting you from a certain type of food be guiding you toward sources of calories that are more fulfilling, or give you a slower release of energy, or providing you with more nutritional benefits, and thus you are more able to live and feel good on fewer calories?

A: That is the goal of many of these diets and some of them tout reasons that they say makes their diet work where others fail. Like with a high-fat diet, the idea is that with fat, you feel fuller and therefore you will eat fewer calories. Other diets – protein-rich, liquid, low-carb, low-sugar, gluten-free – have their own strategy. But most diets can find an explanation for why using their system will enable you to tolerate fewer calories per day.

Q: And here’s where we get to the data. I know you’ve been following the research on these diets for a while. Theories are one thing, but the data doesn’t lie. What does the data say about these diets?

A: You’re right. There is data, and the data is objective. It doesn’t care what theory you’re selling about why your diet should work. And the data shows that with all the diets, less than one percent of fad dieters can maintain that weight loss for more than a year. Another thing that the data shows is that the average weight loss for these diets is around five percent, which is not a lot. So if a 200-pound person was looking to drop fifty pounds that may be an unrealistic weight loss goal. Somewhere around a ten-pound weight-loss goal may be more realistic looking at long-term weight loss using that particular diet.

Q: And that means staying on that diet long-term, just to avoid gaining that 5% of your weight back? That sounds demoralizing.

A: Exactly. Therefore, if you are expecting more than the average weight loss you are going to have to be more aggressive and maintain it for longer than the average person.

Q: How about those healthy frozen dinners? Nutritional value, good replacement for fast food, what’s not to love?

A: Well, they do help with portion control, and they are convenient, and a lot of really unhealthy food is convenience food. So those are good things. But I would limit your intake of those frozen dinners, even lower-calorie ones, because they are often high in other harmful things, like salt, for its preservative value.

Q: What about the types of diets that give you a supplement or something else designed to help you not be hungry or keep you from wanting to eat so many calories? Would you recommend those as an additional aid, to help with portion control?

A: Most of the supplements on the market work in one of two ways. Some reduce the absorption of your food so you can eat more, but it will pass through your body, and you are not going to reap the benefits of having eaten it, or have the side effects of having consumed those calories. The other type of supplement increases your metabolism to help your body burn calories you’ve eaten. However, the supplement that increases your metabolism can also put an increased strain on the heart. That’s why those that alter your metabolism come and go from the market in such a faddish way: They generally put the user at an increased risk of heart attack, and they only last on the market for a short time long enough for those cases to accrue.

The other problems with the supplements are that you are depending on that supplement for life, which can get quite expensive, or as soon as you stop taking the supplement, you go back to your prior weight.

Q: So what actually works, long-term?

A: If you want to be in that one percent, which are the people who are able to lose weight and maintain it for more than a year, there’s one rather large study that looked closely at long-term weight loss. It shows you some of the characteristics of the people who do lose the weight and maintain it. Those people are more successful because they are using a less-restrictive diet. They are also eating more frequent meals. Most of them ate up to five times a day, but they were eating lower-calorie meals, with each meal averaging about 400 calories – far below the average calorie count per meal for the average American. They also all kept track of how they were doing by weighing themselves daily. By objectively measuring themselves every day, there was no guessing as to whether they were doing good or bad on their diet.

Those who were successful also exercised regularly. By maintaining a regular exercise program, they were not only able to keep the weight off, but they were also able to compensate for sometimes eating more calories than their average daily calorie count. That means they could accommodate things they really wanted, while still sticking to their overall plan. That is huge for sticking with diets. Those dieters could do an extra thirty minutes of exercise to burn those extra calories that they consumed. Those are the big factors that they had in common that made them a part of that one percent. And the good news is, these are lifestyle changes that anyone can make. You don’t need a pill, you don’t need a new designer diet. You need to reduce your portions, you need to lower your caloric intake, and you need to exercise. It won’t come up often in the news, because it isn’t “news.” But it’s what works.

— Jeremiah McNichols

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