Comparison Of Weight-Loss Diets, Low-Fat Or Low-Carb?

According to this recent study, it doesn't matter:

Comparison of Weight-Loss Diets with Different Compositions of Fat, Protein, and Carbohydrates, New England Journal of Medicine, February 26, 2009

I did learn something though: Weight loss - no matter how you get there - improves markers for health.

The study ran for 2 years, a little longer than other studies of its kind. Here were their goals:

Click for larger.
I don't see anything extreme, except for the last one, Diet 4, which held carbs to 35%. That would be unusual for the Average American unless they were making a concerted effort. Even then, it doesn't cut carbs as low as today's popular low-carb diets do.

By the same token, those 2 low-fat diets (Diet 1 and Diet 2) don't cut fat as low as popular low-fat diets do. Still, I would expect that if the participants really ate their chosen diet, and if macronutrients really play a role in weight loss, some trend would emerge. No trend did, not that reached significance.

The authors concluded:

"Reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize."

They claimed that social support was more important than what people ate:

"Attendance [at group and individual counseling sessions] had a strong association with weight loss, and the association was similar across diet groups."

"These findings together point to behavioral factors rather than macronutrient metabolism as the main influences on weight loss."

Other Findings

Participants, on average, began to regain lost weight after a year, regardless of diet. (And they were getting a lot of reinforcement! See below.)

Participants had a tough time adhering to their protein/fat/carb prescription:

• The low-fat people ate more than 20% fat (more like 27%).
  
• The high-fat people ate less than 40% fat (more like 34%).
  
• The high-carb people ate less than 65% carb (more like 58%).
  
• The low-carb people ate more than 35% carb (more like 43%).

All participants:

• Received group and individual counseling sessions at least 2x/month for 2 years.
  
• Received a diet that was 750 calories less than that needed to maintain their current weight (goal). Actual decrease was less, from 200 to 500 calories.
  
• Exercised 90 minutes/week (goal).
  
• Kept daily food records.
  
• Almost 70% of participants were college graduates.

When you look beyond weight loss, at 2 years all of the following markers for health improved, regardless of diet, with trends noted:

• LDL: Diets 1 and 2 decreased LDL more than Diets 3 and 4.
  
• HDL: Increased most in Diet 4.
  
• Fasting Insulin: Decreased most in Diet 2.
  
• Urinary nitrogen: Decrease in urinary nitrogen was least for high-protein groups. Decreased most in Diet 1.
  
• Triglycerides decreased similarly.
  
• Blood pressure decreased similarly.

Here's something I thought was strange - everyone's fasting glucose went up, regardless of diet. It increased the most in the high-fat groups, with the high-fat/high-protein group (Diet 4) rising the most. I wouldn't say the rise was clinically significant, but the direction, given weight loss, was unexpected for me.

I liked this quote:

"When nonnutritional influences are minimized, as they were in our study, the specific macronutrient content is of minor importance, as was suggested many years ago."

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