Jason Boehm examines the evidence — or lack thereof — backing the diets ranked by US News & World Report
In part one of our three-part series, we reviewed the rankings of 38 eating plans, issued annually by U.S. News & World Report.
What does science actually say — if anything — about these plans?
Unfortunately, few of the 38 diets reviewed by the U.S. News & World Report (USNWR) expert panel have received significant research.
The experts who evaluated 38 diets for U.S. News & World Report (USNWR) pointed out obvious flaws in some plans.
For example, they rightly scold the Ornish Diet for being ultra-low fat, when research is showing that that’s a pretty bad idea, both for health and the ability to maintain the diet. As USNWR said, “Dieters have a hard time sticking to a plan that restricts fat to 10 percent of daily calories.”
But the USNWR panel sometimes oversimplified things or got them wrong.
“Losing weight is as simple as restricting calories, fat and portions,” they say about Jenny Craig, even if it isn’t really that simple.
In fact, a compelling body of recent research suggests that while calories matter, their source matters as well.
Recent evidence reviews ranked commercial plans on results
In line with conventional wisdom — which holds that weight loss boils down to calorie-cutting — most of these plans provide smaller-portion, therefore lower-calorie meals.
There's no doubt that — at least in the short term — low-calorie diets reward users with quick results, and very-low-calorie diets provide even faster results.
But, as one researcher wrote, “Whether patients value the modest weight loss produced by these programs enough to absorb the financial cost and sustain behavioral change is also unclear.” (Wee CC 2015).
Earlier this year, researchers from Johns Hopkins University reviewed three randomized, controlled clinical trials that tested leading commercial weight loss plans against each other. Each trial lasted at least 12 weeks.
And the trials detected little difference: "There is limited evidence that any one of the commercial weight-loss programs has superior results for mean [averge] weight change, mean waist circumference change, or mean blood pressure change." (Vakil RM et al. 2016)
A similar evidence review published last year examined 39 randomized controlled trials (Gudzune KA et al. 2015).
In each case, the diet in question was compared to receiving education and/or counseling.
Only the trials that tested the Atkins, Weight Watchers, and Jenny Craig diets lasted a full year:
- Atkins resulted in 0.1–2.9% greater weight loss.
- Weight Watchers’ resulted in at least 2.6% greater weight loss.
- Jenny Craig resulted in at least 4.9% greater weight loss.
Studies on these diets only lasted three months:
- Results for SlimFast were mixed.
- Nutrisystem participants resulted in at least 3.8% greater weight loss.
- Very-low-calorie programs (HMR, Medifast, Optifast) resulted in at least 4.0% greater short-term weight loss, but, in studies that lasted six months, the effect faded after that point.
It seems safe to say that there were no clear winners among these popular plans.
More on Weight Watchers
It’s worth focusing on Weight Watchers, because it was ranked number one for Best Weight Loss Diets by the USNWR panel.
Overall, most studies reported positive results about this popular diet.
Other studies show that — compared with going it alone — people doing Weight Watchers lose more weight, which isn't at all surprising.
However, as we noted above, evidence reviews haven't found any significant weight-loss advantages for people doing Weight Watchers versus other commercial plans.
One study found that the percentage of lifetime Weight Watchers members who maintained at least five percent of their weight loss one, two, or five years after successful completion of the program was 79.8, 71.0, and 50.0, respectively.
The plan’s points system for foods clearly works for some people, and Weight Watchers correctly advises people to avoid sugars.
Where they misstep is demonizing saturated fat: a position that fails to recognize the widely varying effects that different saturated fats exert on the body.
For example, the health effects of the saturated fats in chocolate and coconut oil differ dramatically from some of the saturated fats in red meats and dairy products. And even some of the saturated fats in red meats — such as stearic acid — do not appear heart-unhealthy.
For more on that topic, see False Advice on Fats? and Big Sugar Paid Scientists to Pin Heart Disease on Saturated Fats.
Commercial liquid/bar food-replacement programs
Some paid plans deliver portion-controlled meal replacements in the form of shakes and bars, which are typically fortified with nutrients (vitamins and minerals) and fibers.
One study found that people who replaced two meals and two snacks daily with liquid shakes and meal bars lost about 16 pounds in three months, compared with about three pounds for those prescribed a diet of conventional foods with a 1200–1500 daily calorie-intake goal.
And the participants who continued to replace one meal and one snack a day maintained an average weight loss of about 23 pounds at 27 months, which is pretty impressive.
Portion control reigns supreme with SlimFast, which USNWR calls “a reasonable approach to dieting with convenient, grab-and-go shakes and bars.”
Other studies found that — compared with an exchange diet plan (EDP) using macronutrient proportions recommended by the American Diabetes Association — people on the SlimFast program lost more weight and achieved lower total and LDL cholesterol levels, and lower levels of glucose, insulin, hemoglobin A1c.
But SlimFast is a reduced-calorie diet, providing just 1,200 per day, so it’s not surprising that people would lose weight in the short-term.
Whether you keep that weight long-term off is another story.
Studies show that people who use meal replacements like SlimFast feel hungrier than people who consume the same amount of calories from solid foods, which satisfy people faster and longer than liquid diets.
(We should note that the Volumetrics diet plan favors foods high in fiber and water, such as vegetables and fruits, because they have fewer calories per ounce and are filling. The same probably isn’t true of meal-replacement shakes, even when they contain added fibers.)
Read their labels and you’ll have second thoughts about meal replacement plans that provide shakes and bars.
The SlimFast Creamy Chocolate Shake contains 180 calories (hardly a “meal replacement”), with a healthy-seeming five grams of fiber, one gram of sugar, and 20 grams of protein.
Yet its ingredients include soy, maltodextrin (corn), sucralose (artificial sweetener), and inferior forms of nutrients, such as synthetic vitamin B9 (folic acid) instead of the natural form (folate).
In reality, none of these meal replacement shakes and bars can possibly match the rounded nutrition of real, whole foods.
Whole plant foods in particular contain wide varieties of antioxidants, fibers, and other beneficial compounds. Some of these enhance our metabolisms and gut microbe populations pretty substantially, via their beneficial “nutrigenomic” effects on our genes.
The DASH, MIND, and Mediterranean diet plans
The DASH and MIND plans – which ranked numbers 12 and 16 respectively for Best Weight Loss Diets and numbers one and two for Best Overall Diets – have been well studied.
DASH was never designed as a weight loss diet, yet studies show it can improve other health factors while helping you lose weight.
One found that the DASH diet could help people lose weight improving blood pressure and insulin sensitivity, but only when combined with a “comprehensive lifestyle modification program” that includes exercise.
And all three appear to boost brain health. A study that looked at the MIND, DASH, and Mediterranean diets found a slower rate of cognitive decline equivalent to 7.5 years of younger age among participants in the top third of MIND diet scores compared with the lowest third.
People who ate a diet close to the MIND plan were 53 percent less likely to develop Alzheimer's disease.
Even people who ate the MIND diet "most" (as opposed to "all") of the time enjoyed a 35 percent reduced risk of developing the disease.
Atkins, Paleo, and other low-carb plans
Definitions of the Paleo diet vary, depending on which advocate you listen to.
We have indications of what our Paleolithic ancestors ate, but the claims on that score exceed the evidence.
For example, many leading advocates call for banning dairy foods, grains, and beans (legumes).
That position may be inaccurate when it comes to beans and grains, and it ignores their proven benefits … see Whole Grain Foods Found High in Antioxidants and Beans Aid Weight and Blood Sugar Control.
And recent findings indicate that some Paleolithic humans ate wild legumes and grains, though those differ significantly from modern hybrids, and were probably eaten in smaller quantities than people eat today.
The USNWR panel deemed the Paleo diet nutritionally unbalanced because most versions eliminate whole food groups.
On the postitive side, all versions of the Paleo diet eliminate processed and refined foods, which lack many nutrients and tend to deliver empty calories.
Of course, that wise restriction also applies to the Mediterranean diet, Dr. Weil's Antiinflammatory Diet, and other plans that focus on whole foods.
And the few existing studies mostly reflect favorably on Paleo-type diets, finding that they deliver weight loss while improving blood sugar and fat profiles.
Importantly, most of the published clinical trials show that low-carbohydrate diets like Paleo and Atkins deliver more weight loss and cardiovascular benefits, compared with low-fat diets.
Interestingly, USNWR did not rank high-fat/very-low-carb "ketogenic" diets, even though such diets show potential for short- and long-term weight loss, and the first phases of some Paleo-type diets, including the Atkins Diet, are ketogenic.
Five limitations of popular plans
To thoroughly critique these diets would require a book, but here are five common flaws and shortcomings:
- Study funding. Read the fine print: As the aforementioned Weight Watchers example showed, some studies are funded by the commercial programs themselves.
- Useless jargon. Many of these plans throw around meaningless, subjective terms like “balanced,” “sensible,” and “moderation.” Experts have been telling people to eat “sensibly” or “everything in moderation” for decades, and today we’re fatter than ever.
- Sustainability. Evaluating how a diet works for years often goes beyond a study’s funding or scope. Almost any program can help you lose weight initially. Sustaining that loss for years isn’t nearly as easy; neither is obtaining the funding for expensive long-term studies.
- Real-world practicality. Portion-controlled meals, bars, and shakes don’t help you navigate the rocky terrain of real-life eating, and tend to get boring. While some plans provide transitional periods, they would also love for you to stay on their product line indefinitely.
- Caloric intake. Low-calorie meal replacement plans such as Medifast and SlimFast will help almost anyone to lose weight initially. But it’s very difficult to maintain a low-calorie diet and almost impossible to maintain a very-low-calorie diet. That’s especially true of meal replacement plans, which provide little variety.
In part 3 of this series, we’ll suggest an approach to eating that delivers truly healthy weight loss and long-term weight control.
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