Diets might actually just work via placebo effect.

Are Diets Just Placebos? The Evidence Is Strange, Funny, and Supports the Theory.

Are Diets Just Placebos? The Evidence Is Strange, Funny, and Supports the Theory.

Health and medicine explained.
July 13 2017 5:50 AM

Are Diets Just Placebos?

The idea is at least worth considering—and it would explain a lot of strange things about how dieting works. 

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Thinkstock

For years, nutrition experts have been trying to figure out the best diet for people who want to lose weight and have more energy. They haven’t been terribly successful. Very few innovations in that field have lasted (beyond eating less and exercising more). Of course, that hasn’t stopped us from trying: There’s the Atkins diet, the all-cabbage diet, the morning-banana diet, the werewolf diet, the Israeli army diet, the Master Cleanse, the Zone, the charcoal cleanse, the alkaline diet, and the baby-food diet, and (my favorite) the Hollywood cookie diet. There’s even a diet that says you will eat less and shed pounds if you just plug your nose while you eat.

While all of these make impressive claims, science has shown again and again that dieting just doesn’t work in the long-term. Most people either don’t lose the weight or see it boomerang right back (for others, the result of dieting is an eating disorder). But still, we cling to diets because we think they will work—or because often, for a short time, for some of us, for that friend-of-a-friend, they do.

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If no diet has turned out to be a silver bullet for weight loss, then what could explain why some of them at least seem to work, at least for some time? In looking at our rampant dieting culture, I realized that there are a lot of elements that remind me of the placebo effects we see in other parts of our lives. And this got me thinking: Perhaps it’s not the contents of the diet that matters. Perhaps it’s simply the act of dieting. Is it possible that, rather than the specifics of the food regime you undertake, it’s the mere act of starting a diet—any diet—that makes you thinner? Could it be that the inherent placebo effect that comes with any diet is what’s causing you to lose weight?

The connection between brain chemistry, eating habits, and weight is nothing new. Our decisions to eat are based on brain chemistry, and the results of those decisions tend to affect our size. We know that stress hormones generated by dieting and other forms of starvation affect how our bodies process fat. Some studies even suggest that deficiencies in certain mood-moderating brain chemicals shape which junk foods we prefer: People with low dopamine crave sweets, those lacking the neurotransmitter acetylcholine crave fat, and those without serotonin try to eat all the starch they can get. So brain chemistry and metabolism are intimately linked.

But could the act of believing that what we are eating will cause weight loss actually be enough to trick our bodies into shedding pounds? It’s a provocative idea but a hard one to test. The tricky thing about placebo effects is that the best way to measure them is through a little, well, trickery—give someone an inert pill, make him think it’s something else, and measure what effect his own beliefs had. I’m not exactly sure what a placebo cookie would look like, but we do have some data from the emerging science of weight-loss medication that can offer an interesting starting point on weight-loss placebos. There are a number of prescription weight-loss drugs on the market, such as orlistat, liraglutide, and sibutramine (which has since been removed because it caused strokes and heart attacks—and, bizarrely, increased appetite). All of them carry side effects and shouldn’t be considered diet pills, but all of them had to pass Food and Drug Administration placebo-controlled trials, too. And while they all out-performed placebo pills, people in the placebo arm still lost an average of five pounds or so over a few weeks or months.

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Now, many of these studies merged the drug with calorie limitations, and just the act of counting calories tends to make people eat less of them. But still, five pounds is enough room for some kind of placebo effect. Similarly, weight-loss supplements get measured against placebo controls (though not as often as they should). In those cases, few if any of them outperform placebos—but people in the placebo arm also lose weight.

So there’s enough circumstantial evidence around diet pills and supplements to think that placebo diets are at least possible. But supplements and drugs aren’t really diets—what would happen if you convinced someone she’s on a diet even though she’s not? The few studies that have been able to devise a true placebo arm for diets have been riddled with bizarre effects, like one Australian study that tried to determine if nonceliac gluten sensitivity is a real thing. In it, subjects reported feeling worse for all kinds of nonsensical reasons, including going from placebo wheat to more placebo wheat.

But as I said before, the best placebo studies involve a little trickery, and thank God a few scientists are willing to go there. The landmark study comes from Alia Crum at Stanford. As a grad student, Crum did an experiment where she found that just telling hotel workers how much exercise they were getting at work could have positive effects on their health. So in 2010, she took the next logical step. She passed out two types of milkshake—a 620-calorie version and a 140-calorie one, complete with labels that claimed they were either indulgent or diet—to two separate groups. As one might expect, the people’s gut chemistry behaved very differently depending on which shake they got, with their hunger hormones (which are also involved in metabolism) dropping much more with the fatty shake.

Except the thing is that she lied—both the shakes were 380 calories. In other words, their bellies responded not to what they were eating but to what they thought they were eating. The following year, a team at Purdue told patients they had invented special solid foods that turned to liquid once in the stomach as well as liquid foods that turn to solid. Some people got actual solids and liquids while others received the magical stomach-changing kinds. Of course, they were actually the exact same meals, and all had the same number of calories.

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Naturally, people could feel the nonexisting transformations. The nontransforming-liquid drinkers were all quickly hungry, while the people drinking the “liquid-to-solid” said things like, “I could barely swallow the liquid it was so thick,” “I am so full I can barely finish the glass,” and my favorite, “It came out like a solid, too.”

Meanwhile the people eating the real solid could barely finish them all while those eating the “solid-to-liquid” said, “It hardly feels like I ate anything,” “It feels like I drank a bunch of liquid,” and “It immediately went away when the cubes turned to liquid in my stomach.”

Giggle all you want, but can you really be sure that given the same situation you wouldn’t feel exactly the same thing? The subjects in an experiment like this aren’t chosen because they are morons; they’re chosen because they are us.

But here’s the stranger bit: Their bodies’ physical chemistry responded accordingly, too. The people who thought they were eating liquids passed them through their systems like liquids. Their hunger hormones, insulin, and other metabolic hormones fell in line with what they expected, not what they ate.

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A similar study showed that key brain regions respond similarly to SoBe Lifewater as a Ben & Jerry’s milkshake, as long as the beverage was offered up with the word treat. Another, announced just days ago from UC–Berkeley, showed that rats that can’t smell gain less weight after eating exactly the same amount of food than rats that can (maybe the nose-pluggers are on to something). No wonder scientists have begun calling our stomachs “the second brain.”

Sadly, there aren’t really a lot more studies picking away at how belief affects dieting, though the Stanford team says more are on the way. The problem, says one scientist who works with Crum, is that most of this work floats between nutrition, psychology, and marketing research, and no one is lining up to pay for it.

There is one more link between placebo effects and dieting: Most placebos (though notably not all) are temporary. And, as so many dieters have learned to their dismay, so are the effects of radical fad diets. As few as 1 percent of dieters will keep the weight off permanently.

All of this reminds me of another hugely popular and powerful industry that trades in fantastical, trendy, and ultimately often temporary health solutions: alternative medicines. I’ve written a book about alternative medicine, and I have nothing against them as long as they don’t damage your body, checkbook, or endangered species. It’s important to remember that like the supplements market, the dieting industry is almost totally unregulated. The kind of diet you create and sell to others is only limited by your imagination. Which makes it more important for consumers to understand how much they might be relying on the placebo effect to impart actual benefits.

There’s plenty more to study when it comes to how our brain understands eating and how our bodies respond to the context around it. Eating is not just a physical act; it’s sensual, cultural, and communal. Does the stomach respond similarly in people who truly love food versus those who see it as just fuel? How are we influenced by the attitudes of the people we eat with? Some of the newest placebo research suggests that placebos can be enhanced by peer pressure. (In one experiment, just knowing people experienced pain relief from a drug correlated with other people feeling unusually high placebo effects.)

Lately, I’ve had the chance to see this in my own life. Recently, at the behest of several family members, I cut gluten out of my diet. It’s my first real diet, and yes, I am aware that gluten is not necessarily bad. But I’ve also felt a little like I’m joining not just my family, but a tribe of gluten-free people across the world, and I’ve dropped about 15 pounds. I have to say that the science is pretty strong that I am just experiencing a placebo effect.

But in the end, do I really care? Sometimes belief is as good as the real thing.

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Erik Vance is a science writer who cover the environment and the brain. His recent book, Suggestible You, is about the power of the mind to affect the body.