Neither option is superior: Cutting either carbs or
fats shaves off excess weight in about the same
proportion, according to the study. What’s more, the
study inquired whether insulin levels or a specific
genotype pattern could predict an individual’s
success on either diet.
The answer, in both cases, was no.
The new study led by Dr. Christopher Gardner of
Stanford University, has shown that it’s the quality
of what you eat - such as emphasizing whole foods
and vegetables - not quantity, which truly impacts
the amount of weight one losses.
Originally, the study set out to look at which diet
might be better – either low-carb or low-fat - and
whether diet success correlated to other factors.
In this randomized clinical trial among 609
overweight adults, weight change over 12 months was
not significantly different for participants in the
healthy low-fat diet group (-5.3 kg) vs the healthy
low-carbohydrate diet group (-6.0 kg), and there was
no significant diet-genotype interaction or
diet-insulin interaction with 12-month weight loss.
About half were men and half were women.
All were randomized into one of two dietary groups:
low-carbohydrate or low-fat.
Each group was instructed to maintain their diet for
In the initial eight weeks of the study,
participants were told to limit their daily
carbohydrate or fat intake to just 20 grams, which
is about what can be found in a 1½ slices of whole
wheat bread or in a generous handful of nuts,
After the second month, Gardner’s team instructed
the groups to make incremental small adjustments as
needed, adding back 5-15 grams of fat or carbs
gradually, aiming to reach a balance they believed
they could maintain for the rest of their lives.
At the end of the 12 months, those on a low-fat diet
reported a daily average fat intake of 57 grams;
those on low-carb ingested about 132 grams of
carbohydrates per day.
Those statistics pleased Gardner, given that average
fat consumption for the participants before the
study started was around 87 grams a day, and average
carbohydrate intake was about 247 grams.
What’s key, Gardner said, was emphasizing that these
were healthy low-fat and low-carb diets: a soda
might be low-fat, but it’s certainly not healthy.
Lard may be low-carb, but an avocado would be
healthier. “We made sure to tell everybody,
regardless of which diet they were on, to go to the
farmer’s market, and don’t buy processed convenience
Also, we advised them to diet in a way that didn’t
make them feel hungry or deprived — otherwise it’s
hard to maintain the diet in the long run,” said
Gardner, who holds the Rehnborg Farquhar
“We wanted them to choose a low-fat or low-carb diet
plan that they could potentially follow forever,
rather than a diet that they’d drop when the study
The study found that those who cut back on refined
sugars and wheat and loaded up on vegetables and
whole foods without regards to portions or exercise,
lost a significant amount of weight.
This strategy worked, regardless of whether the
study participants were in the low-fat or low-carb
camps, or whether they had possible insulin
resistance or genetic markers.
Perhaps the biggest takeaway from this study,
Gardner said, is that the fundamental strategy for
losing weight with either a low-fat or a low-carb
approach is similar. Eat less sugar, less refined
flour and as many vegetables as possible.
Go for whole foods, whether that is a wheatberry
salad or grass-fed beef.
“On both sides, we heard from people who had lost
the most weight that we had helped them change their
relationship to food, and that now they were more
thoughtful about how they ate,” said Gardner.
For more information
Effect of Low-Fat vs Low-Carbohydrate Diet on
12-Month Weight Loss in Overweight Adults and the
Association With Genotype Pattern or Insulin
SecretionThe DIETFITS Randomized Clinical Trial