Mediterranean, Low Carb and Low Fat Diets: A Six Year Review

In a letter published in the New England Journal of Medicine today, researchers updated us on the results of the famed Dietary Intervention Randomized Controlled Trial (DIRECT) study (link in references below). If you don’t remember, the DIRECT study tested a low carb, low fat, and Mediterranean diet over 2 years.  At the two year mark, these were the results for weight loss:

  • −2.9±4.2 kg for the low-fat group
  • −4.4±6.0 kg for the Mediterranean-diet group
  • −4.7±6.5 kg for the low-carbohydrate group


Yes, at two years, the low carb group had lost slightly more weight than the Mediterranean group, and both groups lost significantly more weight than the low fat group.

The original study measured more than just weight though. It found other notable changes as well: all groups reduced systolic and diastolic blood pressure (low fat group had the largest reduction, low carb group had the smallest reduction), reduced triglycerides (low carb group had a tremendous drop, low fat group was significantly less), reduced C-Reactive Protein (C-RP) levels (huge drop in low carb, slightly less in Mediterranean, low fat did not have a significant change), etc…

So, what would you expect after an additional four years?  A continuation of these trends?  Well, for many of them, yes. But apparently not for weight loss…

According to the letter, after 6 years, people in the low carb group regained 4.1kg, people in the low fat group regained 2.7kg, and people in the Mediterranean group had regained only 1.4kg. So, while the low carb group initially lost the most weight at the 2 year mark, at the 6 year mark they also regained the most.  At the end of the day, however,

as compared with the weight at baseline, the 6-year weight loss was significant for the Mediterranean group (P<0.001) and the low-carbohydrate group (P=0.02) but not for the low-fat group (P=0.28).

It’s more than just weight though. At six years the reduction in triglycerides “were significant in the Mediterranean group (21.4 mg per deciliter [0.24 mmol per liter], P=0.03) and the low-carbohydrate group (11.3 mg per deciliter (0.13 mmol per liter], P=0.02)”, but not for the low fat group.

So what do we make of this?

Well, the Mediterranean diet was the clear winner as far as weight loss goes, but there were clearly additional benefits to both the low carb and Mediterranean diet at six years, despite regaining weight. Also, it’s worth noting that despite the regain in weight for the low-carb group, it still had significant weight loss after six years.  Interestingly, despite having the lowest amount of weight regained, the low fat group did not have significant weight loss at six years.

While the low carb diet was not the “winner” in terms of weight loss the followup shows that it is clearly a healthy and beneficial way of eating.  Perhaps the authors of the followup letter put it best:

In conclusion, a 2-year workplace intervention trial involving healthy dietary changes had long-lasting, favorable postintervention effects, particularly among participants receiving the Mediterranean and low-carbohydrate diets, despite a partial regain of weight.

If you have any thoughts on this study, or the followup I’d love to engage in the comments below!

References

3 Responses to “Mediterranean, Low Carb and Low Fat Diets: A Six Year Review”

  1. The obvious question on weight regain is always was it a failure of the diet, or a failure to stay true to the diet?

    Is this addressed anywhere in the data? As we know “carb creep” can sometimes be inevitable.

    Reply
  2. mjoneill

    Excellent question, Danny!

    It’s not addressed at all in the followup. According to the supplemental information, this is what they did:

    We used one question: Are you still dieting? The question had three possible answers to choose from: 1. “Yes, with my original diet” 2. “Yes, but I switched to another diet” 3. “No, I am not dieting”. No differences were observed in response to this question between the 3 assigned diet groups (p=0.36).

    They do NOT say explicitly that they excluded people based on their answers. So, from what I’ve seen, there is no way to account for what’s responsible for the increase. I would speculate that it’s a non compliance issue from carb creep, or not sticking to the plan, etc… But there appears to be no way to tell from the information provided.

    Reply

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