Obesity prevention by CR

[Guest guest]

Hi All,

The attached is PDF-available and to my liking, especially the last

paragraph:

" The recipe for effective weight loss is a combination of motivation,

physical activity, and caloric restriction; maintenance of weight loss is a

balance between caloric intake and physical activity, with lifelong

adherence. For society as a whole, prevention of weight gain is the first

step in curbing the increasing epidemic of overweight and obesity. Until

further evidence is available regarding the long-term benefits of a

low-carbohydrate approach, physicians should continue to recommend a healthy

lifestyle that includes regular physical activity and a balanced diet. "

Cheers, Al, email: apater@....

New Engl J Med, 348: pages ?-?. Diet, Obesity, and Cardiovascular Risk

O. Bonow, M.D., and H. Eckel, M.D. (2003).

The growing prevalence of obesity and type 2 diabetes in the United States has

attracted

the attention and concern of the medical profession, the media, policymakers,

and the

American public. Recent statistics from the Centers for Disease Control and

Prevention

indicate that nearly two thirds of American adults are overweight (body-mass

index [the

weight in kilograms divided by the square of the height in meters], greater than

25) and

more than 30 percent are frankly obese (body-mass index, greater than 30), that

nearly 8

percent are diabetic, and that 24 percent have the metabolic syndrome. The

metabolic

syndrome is an ominous combination of visceral obesity, atherogenic dyslipidemia

(low

levels of high-density lipoprotein [HDL] cholesterol and elevated levels of

triglycerides),

hypertension, and glucose intolerance that contributes to insulin resistance and

a heightened

risk of diabetes and cardiovascular disease.

These troubling trends have emerged over the past few decades, during which

there has

been a striking increase in caloric intake and a decrease in physical activity

in the U.S.

population. These trends have also spawned a number of best-selling books based

on

popular diet theories, many of which suggest that altering the macronutrient

composition of

the diet can make it easier to curb caloric intake (or even to induce weight

loss without

reducing caloric intake) and can help reduce the risk of heart disease,

diabetes, and other

diseases. Principal among these dietary approaches are those promoting

high-protein,

low-carbohydrate regimens (e.g., the Atkins diet), which have gained widespread

popularity even though the scientific evidence supporting their safety and

efficacy is limited.

A recent review of low-carbohydrate diets reported that weight loss with these

diets is

related to the duration of the diet and the restriction of calories but not to

the reduction in

carbohydrate intake per se and also pointed out the paucity of long-term data.1

In only five

published investigations were subjects following these diets studied for longer

than 90 days,

and none of the studies were randomized or included a comparison group.

The studies reported by Samaha et al. and et al. in this issue of the

Journal (pages

2074–2081 and 2082–2090, respectively) extend knowledge about low-carbohydrate

diets. Each group of investigators randomly assigned obese subjects to either a

low-carbohydrate diet (with high protein and fat

content) or a more standard, reduced-fat diet (with fat constituting less than

30 percent of the total caloric intake but more than

in some extremely low-fat diets). Each study was designed to follow subjects for

more than 90 days. Samaha et al. followed

severely obese subjects (mean body-mass index, 43) with a high prevalence of

diabetes (39 percent) or of the metabolic

syndrome without diabetes (43 percent), whereas et al. studied subjects

with less severe obesity (mean body-mass

index, 34), none of whom had diabetes. Samaha et al. used fixed-carbohydrate

restriction (30 g or less per day), and et

al. used the Atkins diet.

Despite these differences in study populations and dietary approaches, both

studies demonstrated significantly greater weight

reduction with the low-carbohydrate diet than with the reduced-fat diet during

the first six months (average reduction, 6 to 7 kg

vs. 2 to 3 kg). However, the magnitude of the weight-loss difference (4 kg in

both studies) was relatively small, and adherence

in the two diet groups was low. In addition, in the study by et al.,

there was no longer a significant difference in weight

loss between the subjects in the low-carbohydrate group and those in the

reduced-fat group at 12 months. This finding could

reflect the small number of subjects remaining in the study at that time or the

possibility that adherence to the diet was low even

among those who continued in the study. Any approach to caloric restriction that

is not compatible with daily lifestyle patterns is

difficult to maintain over the long term.

In both studies, the reduction in serum triglyceride levels in subjects randomly

assigned to the low-carbohydrate diet might have

been anticipated as a result of their greater weight loss, although it is true

that reduced carbohydrate intake is generally

associated with reduced triglyceride levels. However, the rise in HDL

cholesterol in the subjects following the

low-carbohydrate diet (a change observed only by et al.) may reflect a

change in HDL subfractions that occurs with

increased intake of saturated fats, and this change has not been shown to be

beneficial. Thus, caution is urged about

overinterpretation of this observation as a beneficial result of a

low-carbohydrate, high-fat diet.

The results of both studies demonstrate that initial weight loss is much easier

to achieve than is long-term maintenance of weight

loss. Even if long-term adherence is possible, there are concerns related to the

long-term use of this diet (see Table), since its

high content of fat (particularly saturated fat) is potentially atherogenic. A

wealth of epidemiologic and nutritional data collected

over the past several decades indicates that the consumption of high levels of

saturated fat has adverse consequences on health.

Low-carbohydrate diets may also lack important vitamins and fiber. Moreover, in

marked contrast to the paucity of long-term

data on low-carbohydrate diets, a number of studies reporting the long-term

effects of reduced-fat diets have been reported.

The Finnish Diabetes Prevention Study Group2 and the Diabetes Prevention Program

Research Group3 demonstrated, in

studies involving obese persons with impaired glucose tolerance, that the

combination of a reduced-fat diet and physical activity

over an average of three years facilitated weight reduction equivalent to that

observed in the two current studies of

low-carbohydrate diets and that this combination also appeared to delay the

onset of diabetes. Data from the National Weight

Control Registry have shown that long-term maintenance of weight reduction can

be achieved with a reduced-fat diet

accompanied by regular physical activity. Moreover, others have shown a

reduction in the rate of death from cardiovascular

causes among persons who consume diets high in fruit and vegetables, whole

grains, and fish. Thus, there is evidence to support

the " heart-healthiness " of a balanced diet consisting of a wide variety of

foods, including fruits and vegetables, whole grains,

legumes, lean meat and poultry, and fish, with the total intake of fat

accounting for less than 30 percent of the total number of

calories and the total intake of saturated fat and trans fat accounting for less

than 10 percent of the total calories.

The recipe for effective weight loss is a combination of motivation, physical

activity, and caloric restriction; maintenance of

weight loss is a balance between caloric intake and physical activity, with

lifelong adherence. For society as a whole, prevention

of weight gain is the first step in curbing the increasing epidemic of

overweight and obesity. Until further evidence is available

regarding the long-term benefits of a low-carbohydrate approach, physicians

should continue to recommend a healthy lifestyle

that includes regular physical activity and a balanced diet.

References

1.Bravata DM, L, Huang J, et al. Efficacy and safety of

low-carbohydrate diets: a systematic review. JAMA

2003;289:1837-1850.[Abstract/Full Text]

2.Tuomilehto J, Lindström J, sson JG, et al. Prevention of type 2

diabetes mellitus by changes in lifestyle among

subjects with impaired glucose tolerance. N Engl J Med

2001;344:1343-1350.[Abstract/Full Text]

3.Diabetes Prevention Program Research Group. Reduction in the incidence of

type 2 diabetes with lifestyle intervention or

metformin. N Engl J Med 2002;346:393-403.[Abstract/Full Text]