Medical Nutrition Therapy for Hypertension and Albuminuria

Lifestyle modifications have been shown to lower blood pressure, enhance effectiveness of antihypertensive drug therapy, and reduce overall cardiovascular risk.^3,4 However, few studies have been carried out exclusively in people with diabetes. Therefore, lifestyle recommendations for people with diabetes are by necessity extrapolated from studies in the general population. Along with the lifestyle modifications discussed below, interventions to stop smoking are of primary importance.

The effects of lifestyle modifications are dose and time dependent and therefore can be greater for some individuals than others and may have greater benefits when combined. It is important for clinicians to know the potential outcomes from medical nutrition therapy (MNT) in the majority of people. Lifestyle recommendations to manage hypertension and their potential to reduce blood pressure are summarized in Table 1.³ 

In people with diabetes, there is a general association between weight reduction and a reduction in blood pressure, but there is a great deal of variability in this response. In almost all weight-reduction studies in the general population, systemic blood pressure is reduced even if the degree of weight loss is small.¹  Overall, the greater the weight loss, the greater the reduction in blood pressure. In a meta-analysis⁵  of 11 weight-loss trials, the average systolic and diastolic blood pressure reductions per kilogram of weight loss were 2 and 1 mmHg, respectively. In the Trials of Hypertension Prevention,⁶  weight loss (goal of 4.5-kg loss) alone or in combination with sodium restriction lowered the incidence of hypertension; however, behavior changes tended not to be sustained over time, thus diminishing the positive effects on blood pressure.

The Dietary Approaches to Stop Hypertension (DASH)Study⁷  evaluated the effects on blood pressure of three dietary patterns: 1) a control diet that was similar to a traditional American diet, 2) a diet high in fruit and vegetables, and 3) the DASH diet, which was higher in fruits, vegetables, and low-fat dairy products and lower in total fat,saturated fat, and cholesterol. Sodium intake, physical activity, and body weight remained constant. Both test diets lowered blood pressure compared to the control diet. However, the DASH diet lowered systolic and diastolic blood pressure by 8 and 6 mmHg, respectively. The diet was effective in all subgroups, although systolic blood pressure in African Americans and hypertensive individuals decreased more than in whites and nonhypertensive individuals.

Although blood pressure response to a reduction in sodium appears to vary widely, when different levels of sodium were used in conjunction with the DASH diet in people with and without hypertension, the lower the sodium intake, the greater the lowering of blood pressure.⁸  The effects were greater in hypertensive individuals, African Americans, and women. Compared to the control diet, which was high in sodium (3.6 g), the DASH diet with its low sodium level (1.2 g) led to a mean systolic blood pressure 11.5 mmHg lower in participants with hypertension and 7.1 mmHg lower in participants without hypertension. The intermediate diet (2.4 g sodium) had an effect between those of the high- and low-sodium diets. Furthermore, the DASH diet and reduced-sodium eating plan has effects similar to single-drug therapy.⁸ 

Several meta-analyses have examined the relationship between sodium intake and blood pressure. A meta-analysis by He and MacGregor⁹  assessed the effect of modest salt reduction on blood pressure in trials with a duration ≥ 4 weeks. A total of 17 trials in hypertensive subjects and 11 trials in normotensive subjects were included. In hypertensive subjects, the decrease in systolic blood pressure was 5.0 mmHg, and in diastolic blood pressure it was 2.7 mmHg. In normotensive subjects, systolic blood pressure decreased 2.0 mmHg, and diastolic blood pressure decreased 0.3 mmHg. The weighted linear regression analyses showed a dose response between the change in urinary sodium and blood pressure. The authors concluded that a modest reduction in salt intake for a duration of ≥ 4 weeks does have a significant and, from a population viewpoint, important effect on blood pressure.

The response to sodium reduction may be greater in subjects who are salt-sensitive, a factor that may apply to many individuals with diabetes.^10,11 Reducing sodium intake can best be done by avoiding processed foods, the source of 75% of sodium intake in the usual diet. Other tips for cutting back on salt (sodium) are listed in Table 2.

Two meta-analyses^12,13 have demonstrated the beneficial effects of exercise on blood pressure. The first analysis¹² showed that walking reduced resting systolic and diastolic blood pressure in adults by an average of 3 mmHg. In the second, in 54 randomized clinical trials, aerobic exercise reduced systolic blood pressure an average of 4 mmHg and diastolic blood pressure 2 mmHg, irrespective of changes in body weight.¹³  Thus,increasing the amount of low- to moderate-intensity physical activity to 30–45 minutes most days of the week is an important adjunct to other lifestyle strategies.

The association between alcohol consumption and risk of chronic hypertension appears to follow a J-shaped curve, with light-to-moderate intake associated with a decrease in cardiovascular risk and excessive and chronic intake associated with an increased risk of hypertension.¹⁴ Moderate intake of alcohol is usually defined as ≤ 2 alcoholic drinks per day for adult men and ≤ 1 alcoholic drink per day for adult women. One drink is defined as 12 oz of beer, 5 oz of wine, or 1 1/2 oz of distilled spirits (∼ 15 g alcohol). A meta-analysis¹⁵  of 15 randomized controlled trials examined the effects of alcohol on blood pressure in heavy drinkers. A reduction of alcohol to moderate intakes reduced systolic and diastolic blood pressure by 3.3 and 2.0 mmHg, respectively.

A meta-analysis¹⁶  of 24 randomized placebo-controlled trials was done to estimate the effect of fiber supplementation on blood pressure. Fiber supplementation (average dose 11.5 g/day) lowered systolic blood pressure by 1.1 mmHg and diastolic blood pressure by 1.3 mmHg. Reductions tended to be larger in older (> 40 years)and hypertensive populations than in younger and normotensive ones. An earlier meta-analysis¹⁷  of 12 randomized controlled trials published before 1995 found a similar effect:an average reduction in blood pressure of 1.2/1.8 mmHg with dietary fiber supplements averaging 14 g/day.

Clinical trials have reported a beneficial effect of potassium supplementation on blood pressure. A meta-analysis¹⁸ found that high dietary potassium intake may help prevent and control hypertension. Most population studies have found no significant relationship between calcium and the prevalence of hypertension. However, a meta-analysis¹⁹ showed a small reduction in blood pressure with the use of calcium supplements. In most clinical studies, magnesium supplementation has been ineffective in altering blood pressure, possibly because of the confounding effects of antihypertensive medications and the short duration of the studies.²⁰  Thus,the role of calcium and magnesium supplementation in preventing or treating hypertension is unknown. Nonetheless, a DASH-type diet that includes fruits and vegetables (five to nine servings per day) and low-fat dairy products (two to four servings per day) will be rich in potassium, magnesium, and calcium and may contribute to a reduction in blood pressure.

More recently, studies have shown that supplementation with large doses of fish oil (median dose of 5.7 g/day) can produce a modest reduction in blood pressure of 2.1/1.6 mmHg, especially in older hypertensive people.²¹ 

The National High Blood Pressure Education Program cautions that some widely publicized approaches have less proven or uncertain efficacy.²² Specifically, they mention calcium and fish oil supplements that lower blood pressure only slightly in individuals with hypertension. In addition, they caution that the ability of herbal and botanical supplements to safely lower blood pressure is unproven, and these products can interact adversely with medications. Lifestyle modifications shown to be beneficial for hypertension management and prevention are summarized in Table 3.

Most encouraging are the trials implementing multiple lifestyle modifications and showing that combining lifestyle interventions can lower blood pressure more effectively than single approaches. Two trials^23,24 evaluated the efficacy of implementing simultaneously multiple lifestyle modifications: sodium reduction, weight loss, the DASH diet, and regular physical activity. The Diet, Exercise, and Weight Loss Intervention Trial²³  randomized hypertensive participants to a lifestyle change or control group. At the end of the 9-week intervention, net reductions in 24-hour ambulatory systolic and diastolic blood pressure were 9.5 and 5.3 mmHg, respectively, and changes in daytime systolic and diastolic blood pressure were 12.1 and 6.6 mmHg,respectively. In the PREMIER trial²⁴  of hypertensive adults, multicomponent, behavioral interventions or multiple behavioral interventions plus DASH were compared to an “advice only” control group. In the multiple behavioral interventions plus DASH group, the mean net reduction in systolic blood pressure was 11.1 mmHg, and in diastolic blood pressure it was 6.4 mmHg. Both studies concluded that in people with hypertension, a comprehensive lifestyle intervention program can substantially lower blood pressure and reduce cardiovascular disease risk.

Research on low-protein diets delaying the progression of renal disease has been controversial. The role of MNT in glucose and blood pressure control is clearly the first priority, but there is some evidence that once albuminuria is present, there may be a beneficial effect on renal function with a reduction of protein to 0.8–1.0 g/kg body wt per day.²⁵  Accurate evaluation and interpretation of protein studies in people with diabetes is difficult because of flaws in design, choice of outcome indicators,retrospective and uncontrolled study designs, unknown state of nephropathy,short-term studies with small numbers of patients, poorly documented adherence to the recommended protein intake, and the limited number of studies in type 2 diabetes. However, despite these flaws, in virtually all reports in subjects with diabetes, renal function improves with a low-protein diet.

A reduction of protein intake in subjects with diabetes and microalbuminuria has been attempted in four studies.²⁵  The achieved protein reduction as measured by urine urea nitrogen ranged from 0.8 to 1.2 g/kg. Even with these small reductions in protein intake, the glomerular filtration rates improved significantly in all four studies, and the albumin excretion rates were reduced significantly in three. In a dose-response analysis, a 0.1 g/kg body wt per day change in intake of animal protein was related to an 11.1% improvement in albuminuria.²⁶ 

Five studies have been done in subjects with diabetes and macroalbuminuria.²⁵ The achieved protein reduction ranged from 0.7 to 0.9 g/kg. Although beneficial effects from the protein restriction were reported, one study²⁷  raised concern that too low a protein intake may cause malnutrition. Patients in the low-protein group reported lower energy intakes and a significant decrease in body weight compared to the control group.

Therefore, although the majority of the studies report that a reduction of protein to 0.8 g/kg body wt per day may slow progression of overt nephropathy,this must be done in the context of overall adequate energy and nutrient intake. Restricting protein intake to 0.6 g/kg requires the use of special low-protein foods. Of concern is the reported malnourishment with the reduced energy intake accompanying the restricted protein intake. Furthermore, there is no strong evidence supporting the benefit of lowering protein to this extent. In macroalbuminuria, there may be additional benefits in lowering phosphorus intake to 500–1,000 mg/day along with the low-protein diet.²⁸  Patients with nephropathy who are hypertensive and edematous may also benefit from a sodium intake that does not exceed 2,000 mg/day.²⁸ 

How do dietitians and educators assist people with diabetes in putting into action the above recommendations for treating hypertension and, when needed,albuminuria? One way is to focus on the nutrition recommendations by implementing the DASH diet, which corresponds to the American Diabetes Association's A-level evidence-based recommendation, “Foods containing carbohydrate from whole grains, fruits, vegetables, and low-fat milk should be included in a healthy diet.”²⁹ Table 4 provides a list of food groups and the number of daily servings to be included in a meal plan of an individual requiring 2,000 cal per day. The number of servings may increase or decrease depending on an individual's energy needs. Individuals also need to heed advice to reduce sodium intake.

Fortunately, carbohydrate counting and the DASH diet mesh well. Many of the serving sizes listed in Table 4are also the equivalent of one carbohydrate serving. Table 5 is a sample day's menu incorporating the DASH diet and carbohydrate counting. The 2,000-calorie menu contains ∼ 1,950 mg of sodium, which is less than the 2,300 mg recommended for the general public but more than the 1,500 mg found most beneficial in the DASH-Sodium trial. It is also much less than the 3,500–5,000 mg of daily sodium that Americans typically average each day, so it is a big step in the right direction of cutting back on sodium. Even getting down to 2,000–3,000 mg of sodium daily, along with eating more fruits and vegetables and low-fat dairy foods, would have a significant blood pressure–lowering effect based on the DASH research data.

Fortunately, eating a lot of produce and dairy foods automatically lowers sodium intake. Very little sodium is found in fresh foods; it is processed items that contain the lion's share, contributing up to 80% of the sodium in most diets. Only 20% comes from the salt shaker on the kitchen table.

Counseling patients with diabetes and renal disease requires a dietitian familiar with MNT for both diabetes and renal disease. Table 6 ³⁰  is an example of a diabetes menu incorporating 40 g of protein, 2,000 mg of sodium, low phosphorus, and carbohydrate counting.

It is estimated that a population-wide reduction in blood pressure comparable to that seen with the reduced sodium DASH diet would result in a decrease of 17% in the prevalence of hypertension, a 6% reduction in the risk of coronary heart disease, and a 15% reduction in stroke and transient ischemic attacks.³¹ High blood pressure can be controlled by weight loss in people who are overweight; being physically active; eating more fruits, vegetables, and low-fat dairy foods; choosing foods lower in sodium; limiting alcohol intake;and, if prescribed, taking antihypertensive medications. All but the last also help prevent high blood pressure. If micro- or macroalbuminuria is present, a modest reduction in protein may slow progression of nephropathy.