Effects of Low-Carbohydrate vs Low-Fat Diets on Weight Loss & Cardio Risk

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Dueling Diets: Low-Carb Equals Low-Fat for Weight Loss but Boosts

Cholesterol

By Judith Groch , MedPage Today Staff Writer

Reviewed by Jasmer, MD; Assistant Professor of Medicine,

University of California, San Francisco

MedPage Today Action Points

* Explain to patients that his study showed that. low-carbohydrate

diets, with their high protein and fat content, are likely to increase

cholesterol levels.

* Note that low-fat diets and low-carb diets were equally

effective for weight loss.

Review

BASEL, Switzerland - Low-carbohydrate and low-fat diets are equally

effective for weight loss, but the low-carb route raises total and

low-density lipoprotein cholesterol levels, according to researchers here.

In a Cochrane-style meta-analysis of five controlled clinical trials,

the investigators found that an increase in total cholesterol and

low-density lipoprotein cholesterol for low-carb dieters offset an

increase in HDL cholesterol and a decrease in triglyceride levels.

The analysis involved trials with 222 individuals on low-carb diets

and 225 on low-fat diets, all with BMIs of 25 or higher, Alain J.

Nordmann, M.D., M.Sc., of University Hospital and colleagues reported

in the Feb. 13 issue of the Archives of Internal Medicine.

The low-carb diets held some advantages at six months, but at 12

months the differences evened out, with a mean difference of -1.0 kg

(95% CI -3.5 to 1.5 kg). There was also no difference in blood

pressure levels between the two groups, Dr. Nordmann said.

Low-carb dieters were restricted to a maximum of 60 grams of

carbohydrates a day without energy restriction. In contrast, low-fat

diets allowed a maximum of 30% of daily energy intake from fat.

At six months, the researchers reported that the low-carb dieters were

more likely to stick with the diet, and they lost more weight than the

low-fat dieters. The weighted mean difference favored the low-carb

group at -3.3 kg (95% CI -5.3 to -1.4 kg).

Beyond six months, there was some good news for the low-carb dieters:

Compared with the low-fat group, their triglycerides were lower with a

weighted mean difference of -22.1 mg/dL (95% CI 38.1 to 5.3 mg/dL).

Desirable HDLs were up at a mean difference of 4.6 mg/dL (95% CI

1,2-10.1 mg/dL).

But on the down side for the low-carb diets, which tend to be high in

protein and fat, LDL levels and total cholesterol were higher compared

with the low-fat diets.

For low-fat dieters, the mean downward change for LDL cholesterol was

5.4 mg/dL (95% CI, 1.2 to 10.1 mg/dL). Total cholesterol was also

better for the low-fat dieters with a mean decrease of 10.1 mg/dL (CI,

3.5-16.2 mg/dL),

the researchers reported.

" Because no trials have yet examined the risk of heart attack or death

in people on low-carbohydrate diets, it's unclear whether the

beneficial effects that low-carbohydrate diets appear to have on HDL

and triglyceride levels cancel out their apparent negative effects on

overall and LDL cholesterol levels, " Dr. Nordmann said.

At 12 months, the differences in weight loss between the two diets

were " minor and not clinically relevant, " the researchers wrote. This

aside, they said, " We believe there is still insufficient evidence to

make recommendations for or against the use of low-carbohydrate diets

to induce weight loss, especially for durations longer than six months. "

" Such diets currently cannot be recommended for prevention of

cardiovascular disease, " they added.

The study was supported in part by Swissmilk of Berne, Switzerland.

Primary source: Archives of Internal Medicine, Feb 13, 2006:166: 285-293

Source reference:

Nordmann, Alain J., M.D., MSc, et al " Effects of Low-Carbohydrate vs.

Low-Fat Diets on Weight Loss and Cardiovascular Risk Factors: A

Meta-analysis of Randomized Controlled Trials. "

http://www.medpagetoday.com/tbprint.cfm?tbid=2664

Effects of Low-Carbohydrate vs Low-Fat Diets on Weight Loss and

Cardiovascular Risk Factors

A Meta-analysis of Randomized Controlled Trials

Alain J. Nordmann, MD, MSc; Abigail Nordmann, BS; Matthias Briel, MD;

Ulrich Keller, MD; S. Yancy, Jr, MD, MSH; Bonnie J. Brehm,

PhD; Heiner C. Bucher, MD, MPH

Arch Intern Med. 2006;166:285-293.

Background Low-carbohydrate diets have become increasingly popular

for weight loss. However, evidence from individual trials about

benefits and risks of these diets to achieve weight loss and modify

cardiovascular risk factors is preliminary.

Methods We used the Cochrane Collaboration search strategy to

identify trials comparing the effects of low-carbohydrate diets

without restriction of energy intake vs low-fat diets in individuals

with a body mass index (calculated as weight in kilograms divided by

the square of height in meters) of at least 25. Included trials had to

report changes in body weight in intention-to-treat analysis and to

have a follow-up of at least 6 months. Two reviewers independently

assessed trial eligibility and quality of randomized controlled trials.

Results Five trials including a total of 447 individuals fulfilled

our inclusion criteria. After 6 months, individuals assigned to

low-carbohydrate diets had lost more weight than individuals

randomized to low-fat diets (weighted mean difference, –3.3 kg; 95%

confidence interval [CI], –5.3 to –1.4 kg). This difference was no

longer obvious after 12 months (weighted mean difference, –1.0 kg; 95%

CI, –3.5 to 1.5 kg). There were no differences in blood pressure.

Triglyceride and high-density lipoprotein cholesterol values changed

more favorably in individuals assigned to low-carbohydrate diets

(after 6 months, for triglycerides, weighted mean difference, –22.1

mg/dL [–0.25 mmol/L]; 95% CI, –38.1 to –5.3 mg/dL [–0.43 to –0.06

mmol/L]; and for high-density lipoprotein cholesterol, weighted mean

difference, 4.6 mg/dL [0.12 mmol/L]; 95% CI, 1.5-8.1 mg/dL [0.04-0.21

mmol/L]), but total cholesterol and low-density lipoprotein

cholesterol values changed more favorably in individuals assigned to

low-fat diets (weighted mean difference in low-density lipoprotein

cholesterol after 6 months, 5.4 mg/dL [0.14 mmol/L]; 95% CI, 1.2-10.1

mg/dL [0.03-0.26 mmol/L]).

Conclusions Low-carbohydrate, non–energy-restricted diets appear to

be at least as effective as low-fat, energy-restricted diets in

inducing weight loss for up to 1 year. However, potential favorable

changes in triglyceride and high-density lipoprotein cholesterol

values should be weighed against potential unfavorable changes in

low-density lipoprotein cholesterol values when low-carbohydrate diets

to induce weight loss are considered.