What is the most effective diet for losing weight?

Cut the calories–and the crap

Kyle May/Flickr

This past weekend, Science-ish was disappointed to read Margaret Wente’s column on health evidence, in which she opined: “Today’s health wisdom has a way of becoming tomorrow’s bunk… This may help explain why all the standard diet and exercise advice is worthless.” Sure, evidence about the best way to eat is evolving, the media screws up reporting on science all the time, and the health sciences are particularly vulnerable to what Edmonton-based health law professor Timothy Caulfield calls, in his insightful new book A Cure for Everything!, “an unprecedented number of perverting influences” like Big Food.

But that’s no reason to discount science altogether. When you look at the evidence about diet, some things are pretty straightforward. So rather than taking a blind approach to a healthy life, Science-ish will stick to the science, and give you the six things you should know about an evidence-based approach to diet and weight loss.

1. Surprise, surprise! There is no “best” diet for losing weight.

Science-ish found research to prove that just about every diet imaginable works when it comes to losing weight. As the authors of this study point out, “Several trials showed that low-carbohydrate, high-protein diets resulted in more weight loss over the course of three to six months than conventional high-carbohydrate, low-fat diets, but other studies did not show this effect… other researchers found that a very-high-carbohydrate, very-low-fat vegetarian diet was superior to a conventional high-carbohydrate, low-fat diet.”

And on and on and on.

Now, this isn’t because the science is necessarily bad or purposefully misleading. It doesn’t mean we should throw our hands in the air and live on chocolate and burgers. The variability in results is caused by a few things: Good studies about the effects of diet need to be long-term and long-term studies are expensive; tracking people over time and getting them to adhere to their assigned diet is difficult; bias sometimes influences the results of the study; and science is an iterative process so things change as research evolves, which—when reported without context—can be confusing.

But, when taken as a whole, the evidence suggests it doesn’t really matter what diet you follow—low carb, high protein, Atkins, whatever. When it comes to losing weight, it’s cutting calories that counts.

Here’s some evidence: this trial looked at long-term results of diets with different ratios of carbohydrates, fat, and protein and found that “the diets were equally successful in promoting clinically meaningful weight loss and the maintenance of weight loss over the course of 2 years. Satiety, hunger, satisfaction with the diet, and attendance at group sessions were similar for all diets.”

Another randomized trial looked at some 300 premenopausal overweight and obese women for 12 months as they each followed one of four weight-loss diets: Atkins (very low in carbohydrates), Zone (low carb), Ornish (very high carb), and LEARN (low in fat, high in carb, based on U.S. national guidelines). Conclusions? Those assigned to the Atkins diet lost more weight and had more favourable outcomes for metabolic effects after one year than the women who went on the other diets. But the implication of this study, researchers suggested, is that weight loss with a low-cab diet is “likely to be at least as large as for any other dietary pattern.”

The journal Public Health Nutrition published a trial comparing the effects of Atkins, the Slim-Fast Plan, Weight Watchers Pure Points program, and the ‘Eat yourself Slim’ Diet and Fitness Plan against a control diet for six months. Participants here were overweight and obese men and women, aged 21 to 60. No difference was observed among the groups at six months, and all groups lost between five and nine kilograms.

The take-home message is pretty simple: when people eat less, and stick to eating less, they will lose weight—no matter the diet. If you want to slim down, figure out a way to eat less that works for you.

2. The basics of a healthy diet are known.

The seemingly ever-changing advice about how to eat is confusing. More avocados, no avocados, some wine, no wine. But it’s confusing because reporters publicize single studies about the details of diet, which change as science incrementally moves along. While the details of a healthy diet are working themselves out, Caulfield told Science-ish, “There has been very little flip flopping on the basics of a healthy diet. We know what it looks like: fruits, veggies, whole grains, lean meats, et cetera.”

He’s not the first to point this out. In recent years, the foodie activist-journalist Michael Pollan as well as as the British debunking doctor Ben Goldacre—among others—have done good work in this area. In particular, I like this Goldacre tirade against the complicating forces of nutritionists: “Diet has been studied very extensively, and there are some things that we know with a fair degree of certainty: there is convincing evidence that diets rich in fresh fruit and vegetables, with natural sources of dietary fibre, avoiding obesity, moderate alcohol, and physical exercise, are protective against things such as cancer and heart disease. But nutritionists don’t stop there, because they can’t: they have to manufacture complication, to justify the existence of their profession.”

3. Cut the crap.

When you’re cutting calories, you need to leave enough room in your diet for those things that your body needs to stay healthy—fruits, vegetables, lean protein—and this means you need to cut the crap. A good place to start is by eliminating all pop, juice, and junk food, Caulfield suggested, adding that half of what’s on your plate should be fruits and vegetables. (Think of Pollan’s famous adage: “Eat food. Not too much. Mostly plants.”)

As Science-ish has noted before, consuming sugary drinks, processed meats, and potato chips has been correlated with weight gain in a previous cohort study while eating vegetables, fruits, nuts and yogurt has been correlated with less weight gain. (Remember, correlation is not causation, but it’s something to think about.) As well, this 2010 Harvard study on sugary beverages and the risk of obesity and type-2 diabetes found that epidemiological reports “clearly indicate that regular consumption of (sugar-sweetened beverages) can lead to weight gain and substantially increase risk of developing chronic diseases including (metabolic syndrome, diabetes, and coronary heart disease).”

Caulfield, an evidence nerd who put himself on a diet to test his theories and lost 25 pounds, put it simply for Science-ish: “We need to eat fewer calories—forever. Not just during the dieting period, but long term. So we need to figure out what we can cut and what you can’t give up. Eat the latter in moderation.”

4. Sticking to a diet is tricky; make a lifestyle change.

Having thrown that “keep it simple” advice out there, Science-ish must acknowledge that doing so is incredibly difficult for us mortals. This trial found it was so difficult to get people to adhere to their prescribed diets, that studying different diets was damned near impossible. “Despite the intensive behavioral counseling in our study, participants had difficulty achieving the goals for macronutrient intake of their assigned group,” the study read.

In a fascinating editorial related to this study, the author notes: “The inability of the volunteers to maintain their diets must give us pause. . . even these highly motivated, intelligent participants who were coached by expert professionals could not achieve the weight losses needed to reverse the obesity epidemic.” The writer goes on to suggest the remedy may be community overhaul, pointing to studies of two small towns in France, in which everyone from the mayor to restaurant owners joined together in an effort to get kids to eat better and exercise more. Over five years, “the prevalence of overweight in children had fallen to 8.8%, whereas it had risen to 17.8% in the neighboring comparison towns, in line with the national trend.”

For now, one message we can take from this is that lifestyle changes are needed to sustain weight loss. As Caulfield told Science-ish, “It is a cliché, but I’ll say it again: it must be a lifestyle change, not a ‘diet.’ ” Science-ish would offer Rob Ford, Toronto’s mayor, that wisdom, as he publicly attempts to lose weight before the summer in a very smart PR trick. Think about the rest of your life, Mayor Ford, not just the summer—or the next election.

5. Tracking helps.

Counting calories may seem retro, and not in a fun way. But those who track what’s going in and frequently weigh themselves have better weight-loss outcomes, which is particularly helpful since studies have found people underestimate calories in the food they eat, especially high-calorie foods.

6. Be aware of the mind-bending forces of industry and culture.

As you have surely noticed by now, there are some evidence-based things we know about what works to help people lose weight. But somehow, the wisdom about what makes us healthy has been twisted to the point that we don’t recognize these simple truths—a statement Caulfield makes very convincingly in his book.

In fact, I wonder whether we’d have a better chance at keeping extra weight off if we had less messaging about junk food around us. Some cities are already taking steps in this direction. But until Mayor Ford’s weight loss regime is extended into a province- and nation-wide health overhaul, Science-ish will leave you with some of Caulfield’s sound advice:

“Be conscious of all the twisting forces that exist in our culture (and within us) that are constantly trying to pull us from a pattern of healthy eating. These forces include our own misconceptions about ourselves and what we eat… Refuse fast food. Don’t get tricked into accepting big portion sizes. Don’t let social pressures—friends, work situations, travel—derail healthy eating. And don’t get bamboozled by the ‘healthy’ or ‘organic’ labels on packaged food. These are, by and large, marketing tools… Simplicity is the revelation.”

After my year-end call for submissions, you told me you were most concerned about two things: whether WiFi poses health risks, and which is the most effective diet for losing weight, based on the evidence. This is the last installment in that series.

Science-ish is a joint project of Maclean’s, The Medical Post, and the McMaster Health Forum. Julia Belluz is the associate editor at The Medical Post. Got a tip? Seen something that’s Science-ish? Message her at [email protected] or on Twitter @juliaoftoronto

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