CLIN. AND EXPER. HYPERTENSION, 21(5&6), 763-768 (1999)

WEIGHT REDUCTION AND OBESITY

Lewis Landsberg, M.D. Department of Medicine

Northwestern University Medical School Chicago, Illinois 606 1 1

Key Words: Blood pressure, diet, insulin, sympathetic nervous system

ABSTRACT

Obesity and hypertension are intimately linked. Weight loss lowers blood pressure and improves the blood pressure response to sodium restriction and antihypertensive medications. In addition to the effects of energy restriction, diets rich in fruits and vegetables (and hence potassium) and rich in low fat dairy products (and hence rich in calcium and magnesium), high in fiber, and low in saturated fat also lower blood pressure independent of sodium and energy content. These dietary modifications, along with weight loss are beneficial in patients only mildly overweight and, because of beneficial effects on other cardiac risk factors should be part of the therapeutic regimen in all obese hypertensive patients.

OBESITY AND HYPERTENSION

The association of hypertension and obesity is well-recognized (1, 2). In

the Framingham Study, the incidence of obesity in the most obese subgroup of the

cohort approached 50% (3). Likewise, a substantial portion of individuals with

essential hypertension are obese. Body fat distribution plays an important

independent role in this association as well (1, 4). The abdominal, upper body fat

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pattern is more closely associated with hypertension than BMI or percent body fat

(1). Recent weight gain is also a very highly significant factor in predicting the

development of hypertension (1, 3). Obesity, moreover, increases resistance to

antihypertensive therapy and interferes with achieving target BP levels (5).

The underlying mechanisms that relate body weight and blood pressure

remain incompletely understood, but insulin mediated sympathetic stimulation

appears to play a role (6). Recent evidence suggests that leptin may also be

involved (7).

EFFECT OF LOW ENERGY DIETS AND WEIGHT LOSS

Both caloric restriction and weight loss have independent, separable

effects on blood pressure (1, 8, 9). Low energy diets reduce blood pressure

without concomitant sodium restriction (lo), although the effects of salt

restriction are additive or synergistic with those of weight loss (11). The

mechanisms involved are not known with certainty, but early in the course of low

energy intake negative sodium balance (natriuresis of fasting) may contribute

along with lowered levels of insulin; with reduction in body fat mass

improvement in insulin sensitivity and diminished sympathetic nervous system

activity (6, 12) are probably involved. Small amounts of weight loss in only

mildly obese patients, can, when combined with sodium restriction, have

clinically important results (1 1, 13, 14).

DIET COMPOSITION

In the last few years impressive evidence from prospective studies has

indicated that, in addition to energy content, mineral and macronutrient

composition influence blood pressure. The well-publicized clinical trial, “Dietary

Approaches to Stop Hypertension” (DASH study) examined the impact of diet

composition independent of energy content in 459 individuals randomized to 1 of

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WEIGHT REDUCTION AND OBESITY 765

3 diets for an 8 week period (1 5) . Energy and sodium content was equivalent in

all 3 groups. As compared with the control (“typical” U.S. diet) a diet rich in

h i t s and vegetables (second group) lowered blood pressure significantly. The

third group, a combination diet, low in total and saturated fat, rich in fruit and

vegetables, and rich in low-fat dairy products produced an even greater fall in

blood pressure (5.5 mm/hg systolic and 3.0 mm/hg diastolic as compared with the

control diet. The blood pressure changes were achieved 2 weeks into the

intervention diet and were sustained for the remainder of the 8 week trial. In the

133 subjects with hypertension (BP greater than or equal to 140 mmhg systolic or

equal to or greater than 90 mm/hg diastolic) the decreases in blood pressure were

substantially greater with a reduction in a systolic of 11.4 and diastolic 5.5 mm/hg

respectively as compared with control diet. Examination of the composition of

the various diets suggests that decreased saturated fat, increased potassium,

magnesium and calcium, and perhaps increased dietary fiber and protein were

associated with the hypotensive effect. This short-term study demonstrates

convincingly that these dietary components, independent of changes of energy

content and sodium, influence blood pressure. Consistent findings were reported

in another 10 week study of subjects with hypertension, dyslipidemia, or diabetes

although in this latter study energy and sodium restriction apparently contributed

to the hypotensive response (1 6).

LONG TERM EFFICACY

Are weight loss and dietary modification feasible long-term strategies in

the treatment of hypertension? Data fiom the Treatment of Mild Hypertension

Study (TOMHS) suggests that over a four year period, weight loss, sodium

restriction, diminished alcohol consumption and increased physical activity can be

sustained, although over time the changes in these variables tend to revert towards

pre-intervention levels (1 3). Blood pressure changes, however, as shown in figure

1 , were sustained in TOMHS over a four year period. Similar results have been

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766 LANDSBERG

TOMHS Lifestyle n=902 Intervention

I Y e a r 4 Y e a r I Y e a r 4 Y e a r

Systolic BP Diastolic BP

Figure 1.

demonstrated in the elderly (1 1). Lifestyle modification, therefore, including

weight loss, exert a modest but clinically significant influence on blood pressure

that is sustained over long periods of time.

SUMMARY

In the treatment of obesity related hypertension caloric restriction and

weight loss play an important role in the overall treatment plan. Obesity is a

significant cause of resistance to antihypertensive therapy and weight loss

increases responsiveness to drugs (5). Increased physical activity facilitates

weight loss, exerts a mild antihypertensive effect, and improves insulin sensitivity

(17). Dietary modification consisting of reduction in saturated fat intake along

with increased intake of potassium, calcium, magnesium, and dietary fiber have

demonstrated efficacy in lowering blood pressure and should exert beneficial

effects on other cardiovascular risk factors. The evidence also suggests that these

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WEIGHT REDUCTION AND OBESITY 767

dietary modiciations may be beneficial in normal weight patients and in those

only modestly obese.

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