A recent study published in the April 2013 issue of the International Journal of Obesity examined whether people would lose more weight on their own (sticking to a prescribed calorie goal) or by eating pre-packaged diet foods that totaled the same number of daily calories. The story was picked up by news outlets with eye-catching headlines like "Packaged diet foods may spur more weight loss, " (Reuters).
Sounds pretty good, right? We thought so, too. So we dug a little deeper to bring out the real truth.
To the untrained eye, it may look like a no-brainer: This pre-packaged diet food plan really works! It must have some kind of special magical nutrition formula or food combination that provides such great results! It's also easy!
Not so fast.
Reuter's lead paragraph is accurate in stating that "In a head-to-head comparison with a traditional diet, people who stuck to a diet of portion-controlled packaged foods lost almost twice as much weight as those who only got advice on how to trim calories." But neither the article, nor the study, explore the reasons why this outcome happened, what may have been flawed about the study, or the fact that the final weight loss of both groups was quite small: 2/3 pound per week for the Medifast group and 1/3 a pound for the control group.
Here are some questions that immediately spring to my mind—and why you should consider these results with a large chunk of salt:
- Were the members of the "reduced-energy, food-based" diet group given any information or tools for tracking calories? You don't need to be a weight loss scientist to know that it will be easier to meet a strict 1, 000-calorie-a-day limit if you're eating prepackaged meal replacements that take the guesswork out of what to eat. In real life, even using a great calorie calculator, estimating and tracking calories is hard—and making decisions about food meal after meal, snack after snack is challenging.
But on the flipside, if you are just given food to eat, and you never truly learn how to make those hard decisions and stick to a healthy diet—any weight loss you earned will be short lived. The second the diet is over, you still don't know how to eat in a way that will sustain your weight loss. You revert back to old habits and the weight creeps back on. It sure didn't make the headline, but after an additional 26 weeks had passed, and subjects were no longer following either diet, the Medifast group members had regained an average of 6.5 pounds, while the control group had regained just 4.4. This shows that those who had to learn it on their own actually fared better in the end. Perhaps a better headline for the story may have been, "Regular dieters who keep weight off longer than people who eat pre-packaged diet foods."
- Nutrition and weight loss studies are hard because the rarely create real-word scenarios like the ones people face day to day when trying to lose weight. For one, study participants are generally paid for their participation in a weight loss study, which is a major incentive to stick with any plan that people don't have in real life. In this study, all the participants on the Medifast plan were provided food FOR FREE as well. This never happens in real life, and the cost of such a plan (about $300 a month) is a major barrier to people being able to start or stick with a program like that.
- Who funded the study? Turns out Medifast, a company that sells pre-packed diet foods and provided them for participants, funded the whole thing. In science as in life we call this a conflict of interest. When a corporation funds a study and signs the paychecks of the researchers conducting it, it's very difficult for anyone involved to be objective. Not only do the researchers have an incentive to give their "employer" the results they want (to ensure the study continues, along with their pay), but that lack of objectivity often trickles all the way down to how the researchers create the study. This study was designed to make Medifast come out on top, by pitting it against another "diet" that really didn't have a chance at winning: telling people to eat less, but not providing them with much help or resources to do so.
I would be more interested in seeing a study that compared these packaged diet foods (which, let's face it, are highly processed and lack fresh food ingredients) to other programs that provide all the food in perfectly controlled portions. And, as even this study showed, what tends to happen when any very controlled diet ends is that the dieter regains at least some of the lost weight. It seems like a more sustainable plan would be to learn healthy eating habits and incorporate them into your life over time until they become routine. A big part of the problem with "diets" of any kind is that there is an implied end date.