CLINICAL
CONTEXT
Good
evidence exists that the Mediterranean diet is associated with salutary
outcomes, including results from the Prevención con Dieta Mediterránea
(PREDIMED) study.[1] This study was a randomized trial of the Mediterranean
diet vs a control condition of advice to reduce dietary fat alone among
patients at elevated risk for cardiovascular events. The main study outcome was
the incidence of major cardiovascular events, and the trial was stopped after a
median follow-up period of 4.8 years because of a preponderance of positive
results.
Compared
with the control group, the hazard ratio for cardiovascular events among the
Mediterranean diet group supplemented with extra-virgin olive oil was 0.70 (95%
confidence interval [CI], 0.54-0.92), and the respective hazard ratio for
participants randomly assigned to the Mediterranean diet supplemented with nuts
was 0.72 (95% CI, 0.54-0.96). The Mediterranean diet appeared effective for
these outcomes regardless of sex, age, and the presence of diabetes.
Nonetheless,
concerns remain about the effects of the Mediterranean diet on obesity and
central adiposity, despite previous research suggesting that the diet can be
effective for weight loss. The current study by Estruch and colleagues revisits
the PREDIMED cohort to investigate how the prescribed Mediterranean diet, which
was not associated with a limitation on calories nor a recommendation for
physical activity, compared with the control diet in the outcomes of body
weight and waist circumference.
STUDY
SYNOPSIS AND PERSPECTIVE
Following
a Mediterranean diet that is not calorie restricted and is high in healthy fats
from olive oil or nuts does not cause weight gain at 5 years compared with a
low-fat diet, according to results from the Spanish PREDIMED randomized
controlled trial.
"These
results have practical implications, because the fear of weight gain from
high-fat foods need no longer be an obstacle to adherence to a dietary pattern
such as the Mediterranean diet, which is known to provide much clinical and
metabolic benefit," write Ramon Estruch, MD, PhD, from CIBER
OBN-University, Barcelona, Spain, and colleagues.
"They
are also relevant for public health, because they lend support to not
restricting intake of healthy fats in advice for bodyweight maintenance and
overall cardiometabolic health, as acknowledged by the Dietary Guidelines for
Americans 2015 Advisory Committee," they add.
The study
was published online June 6 in Lancet Diabetes & Endocrinology.[2]
The study
is the first randomized trial to evaluate the long-term effects of an
unrestricted-calorie Mediterranean diet on weight and waist circumference.
Much
evidence has linked a Mediterranean-style diet high in vegetable fats such as
nuts and olive oil to decreased risks for all-cause mortality, cardiovascular
disease, and cancer.
For the
past 40 years, however, standard dietary advice for preventing or treating
obesity has called for calorie restriction and increased physical activity,
with a persistent belief that high fat intake promotes weight gain. Such recommendations,
however, have not necessarily taken into account the different types of fat.
Nonetheless, certain scientific societies -- including the World Health
Organization[3] -- continue to advise limiting fat in the diet.
The idea
that all dietary fat is unhealthy has led many US adults to curb their fat
consumption, often at the expense of eating empty calories from processed foods
high in sugar, salt, and carbohydrates. The demonizing of all fat, though, has
failed to stem the tide of the diabetes and obesity epidemic.
The
PREDIMED randomized controlled trial took place in primary care centers
connected to 11 hospitals in Spain between 2003 and 2010. It included 4282
women 60 to 80 years old and 3165 men 55 to 80 years old with type 2 diabetes
or 3 or more cardiovascular risk factors. All patients were asymptomatic, and
more than 90% were overweight or obese at baseline. They had a mean age of 67
years; 97% were of white European ethnicity.
Researchers
randomly assigned participants to an unrestricted-calorie Mediterranean diet
with extra-virgin olive oil (n=2543), an unrestricted-calorie Mediterranean
diet with nuts (n=2454), or a low-fat control diet (n=2450). Trained dieticians
gave dietary advice to all 3 groups. Participants were not advised to restrict
calories or increase physical activity.
Participants
received free polyphenol-rich extra-virgin olive oil and nuts (walnuts,
almonds, or hazelnuts). Results showed good adherence in the olive oil and nut
groups, based on self-reported questionnaires, and blood and urine samples in a
random subgroup.
Five-year
results showed that total fat increased in the 2 Mediterranean diet groups.
Both Mediterranean diet groups actually had a slight increase in fat
consumption -- from 40% to 41.8% in the olive oil group and 40.4% to 42.2% in
the nut group (P <.0001 for all) -- while their consumption of protein and
carbohydrate decreased (P <.0001).
All 3
groups lost a small amount of weight. At 5 years, the olive oil group lost the
most weight (0.88 kg), followed by the low-fat control group (0.60 kg), and
then the nut group (0.40 kg). Multivariable analyses adjusted for 12 potential
confounders showed that the difference in weight change at 5 years was
significant only for the olive oil group vs the control group (P =.044).
Likewise,
all 3 groups had a slight increase in average waist circumference, but the
increase was smaller for the Mediterranean diet groups (low-fat control group,
1.2 cm; olive oil group, 0.85 cm; nut group, 0.37 cm). Multivariable analyses adjusted
for 12 potential confounders showed that the difference in change in weight
circumference at 5 years was significant for both the olive oil and nut groups
vs the control group (P =.048 and P =.006, respectively).
In a
linked comment,[4] Dariush Mozaffarian, MD, DrPH, from the Friedman School of
Nutrition Science and Policy at Tufts University, Boston, Massachusetts, writes
that these results provide "further robust evidence that liberally adding
healthy foods to the diet, including high-fat choices such as nuts and
extra-virgin olive oil, does not increase weight gain."
"These
important findings should be heralded around the world," he asserts, while
calling for the revision of dietary guidelines.
Decades
of dietary advice have ignored food quality and the different effects of
specific fatty acids, he pointed out.
By
emphasizing calorie and fat restriction, such advice has produced
"paradoxical warnings and caveats about eating healthy, high-fat foods"
and fostered the proliferation of low-fat foods -- often high in sugar and
carbohydrates -- in the US diet.
"[M]odern
scientific evidence supports an emphasis on eating more calories from fruits,
nuts, vegetables, beans, fish, yoghurt, phenolic-rich vegetable oils, and
minimally processed whole grains; and fewer calories from highly processed
foods rich in starch, sugar, salt, or trans-fat. We ignore this evidence --
including these results from the PREDIMED trial -- at our own peril," he
concludes.
CLINICAL
IMPLICATIONS
- The PREDIMED trial demonstrated that a Mediterranean diet supplemented with extra-virgin olive oil or nuts reduced the risk for incident cardiovascular events among high-risk patients, regardless of age, sex, or the presence of diabetes.
- The current study by Estruch and colleagues demonstrates that the Mediterranean diet was not associated with weight gain compared with a low-fat diet in older adults at high cardiovascular disease risk. The Mediterranean diet provided a slight benefit in waist circumference compared with the control diet.
- Implications for the Healthcare Team: The Mediterranean diet is not only effective in reducing the risk for cardiovascular disease, but the current study suggests that it may reduce central adiposity as well. Moreover, it is one the more palatable healthy diets for many patients. The healthcare team should focus on how to add elements of the Mediterranean diet among at-risk patients.
Veronica
Hackethal, MD
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