New study compares healthiest diets

By John Murphy, MDLinx
Published April 14, 2020

Key Takeaways

There’s no secret to losing weight. Just eat healthy and get exercise. But, what really constitutes “eating healthy”? (We’ll save “get exercise” for another article.) Dietary advice seems to change every week, so it's no wonder that Americans are confused about what eating healthy means. Does it mean “low fat” or “low carbs”? Or is it “more plants” or “more protein”? Is red meat healthy or unhealthy? Which diet is best? Atkins? Mediterranean? Ornish? Paleolithic? Weight Watchers? 

To get to the bottom of it all, a team of researchers from the United States, Canada, and around the world compared 14 name-brand diets to see which is the best at reducing weight loss and improving cardiovascular risk. What they found...well, what they found is that it’s not so easy to identify one single diet over the rest. 

Apples to apples

The prevalence of obesity in the world has nearly tripled since 1975. More than ever, people are looking for a way to lose weight by changing their diets. 

To that end, these researchers performed a systematic review and meta-analysis of 121 randomized clinical trials comprising 21,942 overweight or obese adults (average age: 49 years). The clinical trials the researchers considered were designed differently and were of varying quality, but they were able to adjust for these attributes in their analysis. 

The researchers compared 14 name-brand diets to the control participants’ usual diets. These included Atkins, Biggest Loser, Dietary Approaches to Stop Hypertension (DASH), Jenny Craig, Mediterranean, South Beach, the Zone, and others. 

The team looked at factors such as weight loss, low density lipoprotein (LDL) level, high density lipoprotein (HDL) level, systolic blood pressure, diastolic blood pressure, and C-reactive protein. Here’s what they found after patients adhered to 6 months of dieting: 

Weight loss. When compared with a usual diet, the most effective diets for weight loss were Jenny Craig (loss of 7.77 kg) and Atkins (loss of 5.46 kg). The least effective diet interventions were The Biggest Loser, Slimming World, and dietary advice.

Systolic blood pressure. Among all the diets, the paleolithic was the most effective (- 14.56 mmHg) at reducing systolic blood pressure, relative to a usual diet. The least effective were the Biggest Loser and the Ornish diets. 

Diastolic blood pressure. Atkins reduced diastolic BP (- 3.30 mm Hg) more effectively than other diets. Paleolithic, Biggest Loser, Mediterranean, and Ornish proved the least effective. Interestingly, the diet specifically designed to lower blood pressure—the DASH diet—was merely better-than-average for lowering systolic and diastolic BPs in this meta-analysis. 

LDL level. Compared with a usual diet, only the Mediterranean diet showed a statistically significant difference in lowering LDL cholesterol (-4.59 mg/dL). Ornish, DASH, Biggest Loser, and low-fat diets were probably no better than the usual diet, the researchers noted. 

HDL level. None of the diets showed a statistically significant increase in HDL cholesterol by the 6-month follow-up.

C-reactive protein. Popular diets were no better than a usual diet for lowering C-reactive protein levels. 

These were the results at 6 months into the diet. But, at 12 months’ follow-up, the researchers found that nearly all these improvements had waned. 

“Weight reduction at the 12-month follow-up diminished, and aside from the Mediterranean diet for LDL reduction, improvements in cardiovascular risk factors largely disappeared,” they wrote. 

What was lost has been found

In terms of weight loss, patients on all diets regained 1.5 kg on average by 12 months compared with the 6-month follow-up. The exception was the paleolithic diet, in which patients continued to lose weight for an average loss of 6.97 kg. 

An honorable mention is the Jenny Craig diet. Although patients regained an average 0.59 kg after 6 months, they lost a total of 7.18 kg at 12 months compared to a usual diet. 

In terms of cardiovascular risk factors, the effects on blood pressure decreased such that the brand-name diets were no better than the usual diet for either systolic or diastolic BP at 12 months. 

The improvements in blood lipids also decreased at the 12-month follow-up—except for the Mediterranean diet, which had a median LDL reduction of 6.17 mg/dL compared with the usual diet at 12 months. None of the diets showed a significant increase in HDL or a reduction in C-reactive protein at 12 months compared with the usual diet.

Bottom line

So, what does all this mean? Which of these diets is the best to follow? 

“Differences between diets are...generally trivial to small, implying that people can choose the diet they prefer from among many of the available diets without concern about the magnitude of benefits,” the authors concluded. 

In other words, don’t worry about which diet you choose. Just “eat healthy” (whatever that means). 

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