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More poorly designed diet research: low-fat vs. low-carb diets
The media has been all over today's study from the Annals of Internal Medicine (doi:10.7326/M14-0180), for the most part acting as if this were the last word on healthy eating. Proponents of the Atkins Diet are understandably celebrating, as the results of the study as published are that a low-carbohydrate diet increases weight loss and improves cholesterol scores more than a low-fat diet.
Live longer (on a cellular level) with a Mediterranean Diet
Back in 2011 I wrote an article about telomeres and omega-3 fatty acids. ... The article linked blood levels of fish- or shellfish-sourced omega-3 fatty acids with the length of the participants' telomeres, showing that more omega-3s meant longer telomeres. Today's research article essentially extends that research.
Not all fats....
When it comes to diet and nutrition, I can understand why people look for simple answers. It's much easier to say "avoid carbohydrates," or "don't eat wheat products," or "all fat is bad" or even "all oils are bad" than to remember to eat fish several times a week, remember which are the best fish, and also keep in mind how much fish is the right amount.
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There's a lot of controversy over which diet is best if you want to lose weight. Low fat? Low carbohydrate? High fat? Mediterranean Diet? DASH (Dietary Approaches to Stop Hypertension)? Weight Watchers? Jenny Craig? Vegetarian? Vegan? Omnivore? Pescetarian? The list is endless, and people will argue for their favorite diet with the zeal of a recent convert.
Studies pop up all the time that seem to show that one type of diet helps people lose weight faster than another type of diet. Just last Fall I shared with you an article that concluded that a low-carbohydrate diet would help you lose more weight than a low-fat diet. Unfortunately, many of those studies (including that one) that compare one diet to another are poorly designed, limit people's food choices in unsustainable ways, or both.
A team at the Veterans Affairs Medical Center in Durham, North Carolina took the approach that rather than being prescribed a specific diet, for the purposes of weight loss alone people might do better and lose more weight if they could choose the diet themselves (Annals Int Med 2015;162:805-814). Makes sense, but as we know, just because something "makes sense" doesn't mean it holds up to controlled trials.
About 200 male and female veterans were recruited from Veterans Affairs patients at the Durham VA. All participants were otherwise healthy but were considered clinically obese (having a Body Mass Index over 30). Half the patients were assigned to a "choice" group and half to a control group.
Those in the Choice group responded to a dietary preference questionnaire, which allowed the staff to recommend a low-carb or low-fat diet as that more closely aligned to their existing preferences. The Choice group participants were then able to choose for themselves which diet they would follow for the next 12 weeks. After 12 weeks following that diet, they were given the opportunity to switch to the other diet if they chose.
Those in the Control group were randomly assigned to either a low-fat or low-carb diet for the duration of the 24-week study.
Both groups received regular personal and group counseling sessions to help with goal setting and problem solving, and the individual's adherence to their assigned or chosen diet was measured by regular dietary questionnaires. Those on a low-fat diet were to consume no more than 30% of their calories from fat and to cut their total caloric intake by about 500 calories per day. Those in a low-carbohydrate diet were to consume no more than 10% of their calories from carbohydrates, but had no specifed calorie restriction.
Very few of the Choice participants decided to switch to the other diet after the initial 12 weeks: only 5 people out of 105 in the Choice group decided they were unsatisfied with their chosen diet plan.
The results are very interesting: those in the Choice group lost, on average, about 5.7 kilograms (about 12.6 pounds), while those in the Control group lost an average of 6.7 kilograms (about 14.8 pounds).
If we're looking at overall weight loss, statistically speaking it didn't matter whether people chose their diet or not - they still lost about the same amount. (Those who cut carbohydrates consumed fewer calories even though they were not directed to do so.) What did appear to make a difference was how many counseling visits people attended: those who attended at least 15 session lost about three times as much weight as those who attended fewer than 15 counseling sessions.
This supports what I've been saying for years: that it's the diet you can stick to for the long term that will work best for you. For some that's low-carb or low-fat or vegan-no-oil, but for the vast majority of people (and as a physician and researcher that's who I'm trying to reach), a Mediterranean-style diet of a variety of high-quality carbohydrates, moderate meats, and lots of fruits and vegetables is the one that is going to allow people to eat what they like while also eating healthy.
First posted: June 24, 2015