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News Brief: Low carb versus low fat diets
September 8, 2014
THE STORY
Low carb diets help the body and heart
The Globe and Mail, September 2, 2014
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A low-carbohydrate diet is better for losing weight and may also be better for lowering the risk of heart
disease than a low-fat diet, according to a new study.
WHERE TO FIND THE RESEARCH
Bazzano LA, Hu T, Reynolds K et al. Effects of Low-Carbohydrate and Low-Fat Diets: A Randomized Trial. Ann
Intern Med. 2014;161(5):309-318. doi:10.7326/M14-0180
A CLOSER LOOK AT THE RESEARCH
Objective: To examine the effects of a low-carbohydrate diet compared with a low-fat diet on body weight
and cardiovascular risk factors.
Participants: 148 men and women aged 22 to 75 years with a body mass index of 30 to 45 without clinical
cardiovascular disease and diabetes. Exclusion criteria: self-reported clinical CVD, type 2 diabetes, or kidney
disease; use of prescription weight-loss medications; surgery; and weight loss greater than 6.8 kg within 6
months of study entry.
The 148 participants were 88% female, 51% black, with mean age 46.8 years.
After randomization, 73 participants were assigned to the low-fat diet group and 75 were assigned to the lowcarbohydrate diet group.
Intervention: A low-carbohydrate (<40 g/d) or low-fat (<30% of daily energy intake from total fat [<7%
saturated fat]) diet. Both groups received dietary counseling at regular intervals throughout the trial.
Participants in each group were asked not to change their physical activity levels during the intervention.
The DOC Network and Dietitians of Canada do not have editorial or other control over the contents of the referenced Web sites. They are not
responsible for the opinions expressed by the author(s) of listed articles and do not endorse any product or service.
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A handbook was given to participants that contained recipes, sample menus for 1 week of food intake at
various energy levels, food lists, shopping lists, meal planners, and guides on counting macronutrients and
reading nutrition labels. A low-carbohydrate or low-fat meal replacement (bar or shake) was provided to
participants in each group every day for the duration of the study.
Participants met with a dietitian in weekly individual counseling sessions for the first 4 weeks, followed by small
group counseling sessions every other week for the next 5 months (a total of 10 sessions) and monthly for the
last 6 months of the intervention. Individual sessions generally lasted about 1 hour and included dietary
instruction and supportive counseling.
Group counseling sessions were held separately for participants in the low-fat and low-carbohydrate groups
but followed a common behavioral curriculum.
Measurements: Two 24-hour dietary recalls were obtained from participants at baseline and 3, 6, and 12
months to characterize and monitor individual dietary intake of macronutrients.
A detailed medical history that included assessment of hypertension, diabetes, CVD, medication use, and
health behaviors (smoking habits, alcohol use, and physical activity) was obtained at the screening visit. Also
collected were anthropometric measures, blood pressure, and blood and urine samples at the screening visit,
randomization, and each follow-up visit.
Results: At baseline, reported dietary composition in the low-fat group was similar to that in the lowcarbohydrate group. At follow-up, total energy intake was similar between groups.
The intake of total carbohydrate was significantly higher and intakes of protein and total, saturated, and
monounsaturated fat (as percentages of kilocalories) were significantly lower in the low-fat group at 12 months
(P < 0.001 for these comparisons). Physical activity levels were similar throughout the study.
The daily dietary composition (means) for each of the groups at 3 and 12 months were:
Three Months
Low Fat
Low-Carb
Twelve Months
Low-Fat
Low-Carb
Energy (kcal)
1418
1258
1527
1448
Carb (% kcal)
193 g (52.9%)
97 g (28.9%)
198 g (54%)
127 g (34%)
Fat (% kcal)
45.3 g (27.5%)
62.6 g (42.7%)
52.4 g (29.8%)
69.0 g (40.7%)
19% kcal
25.6% kcal
18.6% kcal
23.6%
Protein
After 12 months, compared to the low-fat group, the low-carbohydrate group had:
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significantly greater weight loss at 3, 6, and 12 months (mean difference -3.5 kg [95% CI, -5.6 to -1.4 kg];
P=0.002). The low-fat group lost 1.8 kg (4 lbs); the low-carb group lost 5.3 kg (11.7 lb)
significantly greater proportional reductions in fat mass (mean difference -1.5% [CI, -2.6% to -0.4%];
P=0.011
significantly greater proportional increases in lean mass (mean difference 1.7% [CI, 0.6% to 2.8%];
P=0.003]
significantly greater decreases in CRP level (mean difference -15.2 nmol/L [CI, -27.6 to – 1.9 nmol/L];
P=0.024)
significantly greater increases in HDL-cholesterol (mean difference 0.18 mmol/L [CI, 0.08 to 0.28
mmol/L]; P<0.001)
The DOC Network and Dietitians of Canada do not have editorial or other control over the contents of the referenced Web sites. They are not
responsible for the opinions expressed by the author(s) of listed articles and do not endorse any product or service.
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significantly greater decreases in ratios of total-HDL cholesterol (mean difference -9.44 [CI, -0.71 to 0.16]; P=0.002
Participants in both groups significantly reduced their waist circumference. Changes in waist circumference
were more favorable in the low-carbohydrate group at 3 and 6 months but did not differ significantly from
those in the low-fat group at 12 months.
At 12 months, serum levels of total and LDL cholesterol had not significantly changed among participants in
either group.
Serum levels of triglycerides decreased significantly in both groups, with greater decreases among participants
in the low-carbohydrate group.
There were no differences in fasting glucose or insulin between groups, with a trend to lower levels in the lowfat group.
THE BOTTOM LINE
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In this randomized, parallel-group trial, the authors concluded a low-carbohydrate diet induced
greater weight loss and reductions in cardiovascular risk factors at 12 months than a low-fat diet
among black and white obese adults who did not have diabetes, CVD, or kidney disease at baseline.
Some of the limitations listed by the authors include lack of CVD clinical end points, the number of tests
performed in the primary analysis means that statistically significant results should be interpreted with
caution particularly P values between 0.01 and 0.05, and the findings may not be generalizable to
more common situations where intensive and repeated dietary counselling is not available. Also, the
results of the subjects’ dietary intake/composition relied on self-reported dietary information which may
be subject to memory issues and the subjects may be more likely to report a diet close to what they
were taught.
The low-carbohydrate group did not achieve the target of less than 40 grams of carbohydrate a day,
however participants did reduce carbohydrate intake from 242 g (48% kcal) at baseline to 97, 93, and
127 g (34% kcal) at 3, 6, and 12 months, respectively. The inability to meet the target suggests the
difficulty of complying and sustaining this restrictive diet. The AMDR for dietary carbohydrate is 45% to
65%; and so this diet would qualify as ‘low-carb’.
The low-fat group achieved the target of 30% of kcal from fat and reduced fat intake from 80.7 g
(34.7% kcal) at baseline to 45, 46 and 52 g (30% kcal). AMDR for dietary fat is 20 to 35%. So, it seems a
misnomer for the researchers to call this ‘low-fat’.
The daily meal replacement used by both groups may have helped them adhere to a lower calorie
intake over time.
The low-carb group had higher protein intake (23.6% kcal vs 18.6% kcal for low carb) which may have
provided greater satiety and helped to reduce overall energy intake leading to greater weight loss.
It is important to note that both groups had the most weight loss in the first 3 months of the study
(calorie difference -190 for low carb over low fat). At 12 months there was a trend for the diets to
becoming closer in calories (-79 calories for low carb over low fat). If this had been a longer study, the
weight difference between both groups may have closed over time.
The above comment is supported by the meta-analysis published last week that concluded “Significant
weight loss was observed with any low-carbohydrate or low-fat diet. Weight loss differences between
individual named diets were small. This supports the practice of recommending any diet that a patient
will adhere to in order to lose weight.”
As dietitians, we should still try to encourage a balanced diet in order to limit nutritional deficiencies.
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can be found on the DOC Network website.
The DOC Network and Dietitians of Canada do not have editorial or other control over the contents of the referenced Web sites. They are not
responsible for the opinions expressed by the author(s) of listed articles and do not endorse any product or service.
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