The DASH diet is designed to reduce blood pressure and improve blood lipids.
It’s typically low in fat and relatively high in carbs, but it’s not clear what role these macronutrients play in the diet’s effectiveness.
For this reason, a group of researchers compared the effects of a higher-fat, lower-carb DASH diet to the conventional DASH diet.
Their results were recently published in the American Journal of Clinical Nutrition.
The DASH Diet Lowers Blood Pressure, Even With More Fat
DASH stands for Dietary Approaches to Stop Hypertension.
It is currently the world’s most popular diet aimed at lowering blood pressure and reducing the risk of heart disease.
The original DASH diet has the following characteristics:
- High in fruits and vegetables.
- High in whole grains and fiber.
- Includes nuts, seeds and legumes several times weekly.
- High in low-fat dairy products.
- Relatively low in red meat, poultry and fish.
- Low in saturated fat, cholesterol and sodium.
- Relatively high in potassium, magnesium and calcium.
- Relatively low in refined sugar.
A large, observational study, called the Nurses’ Health Study, found a DASH-type diet to be associated with a reduced risk of heart disease and stroke.
Some researchers believe that the DASH diet may reduce heart disease risk because of its low saturated fat content.
However, this idea has not been put to the test.
A team of scientists from the Children’s Hospital Oakland Research Institute, in California, compared the effects of the standard DASH diet and a higher-fat, lower-carb DASH diet on blood pressure and blood lipids.
Basic Study Design
This randomized, controlled trial examined the effects of a modified DASH diet and the standard DASH diet on blood pressure and blood lipids. The modified diet included more dairy fat and fewer carbs.
The participants were healthy men and women with systolic blood pressure less than 160 mm Hg, and diastolic blood pressure between 80 and 95 mm Hg.
The participants were assigned to three groups in random order:
- Standard DASH diet: Participants followed the conventional DASH diet.
- Higher-fat DASH diet: This diet included more dairy fat and less carbs, but was otherwise identical to the standard DASH diet.
- Control diet: The control diet was designed to represent a normal Western diet.
In the higher-fat DASH diet, the saturated fat content was increased from 8% to 14% of daily calories. To keep the calorie content the same, the carb content was also reduced by 12% of daily calories.
Each of these diets lasted for 3 weeks. The study had a crossover design, meaning that all of the participants followed all three diets during different study periods, separated by a 2-week washout period.
At the beginning and end of each of the three diets, the researchers measured blood pressure, blood lipids, body weight and body fat.
A total of 36 participants completed the study.
Bottom Line: This randomized, crossover trial examined the effects of a higher-fat, lower-carb DASH diet on blood pressure and blood lipids.
Finding 1: Dairy Fat Did Not Adversely Affect Blood Pressure
Both the standard DASH diet and the higher-fat DASH diet reduced blood pressure to a similar extent, compared to the control diet, as shown in the chart below.
However, blood pressure was significantly lower two weeks after the participants had finished the higher-fat DASH diet, suggesting delayed effects.
This means that eating more saturated dairy fat on the DASH diet does not adversely affect blood pressure.
Other studies have found that modifying the standard DASH diet by replacing carbs with unsaturated fat or protein yields similar or greater improvements in blood pressure.
Bottom Line: The standard DASH diet and the higher-fat DASH diet reduced blood pressure to a similar extent, compared to the control diet.
Finding 2: Higher-Fat DASH Diet Reduced Triglycerides
The DASH diet and the higher-fat DASH diet had different effects on the blood lipid profile. The higher-fat DASH diet reduced the levels of triglycerides, as shown in the chart below.
This modest reduction in triglycerides may be explained by the lower amounts of carbs in the higher-fat DASH diet, compared to the standard DASH diet.
Bottom Line: The higher-fat DASH diet reduced triglycerides, compared to the standard DASH diet, due to the lower carb content of the higher-fat diet.
Finding 3: Effects on LDL Peak Diameter
High levels of small, low-density lipoproteins (LDL) have been associated with an increased risk of heart disease.
In the present study, the conventional DASH diet reduced the peak diameter of the LDL particles, but the higher-fat DASH diet increased the peak diameter, compared to the control diet.
This means that the higher-fat DASH diet may have caused a modest increase in LDL particle size.
In fact, there was a trend for higher levels of large LDL particles with the higher-fat DASH diet, but the findings were not significant.
Previous studies have shown that reduced carb and sugar intake may cause a shift from smaller to larger LDL particles, explaining the present findings.
Bottom Line: The higher-fat DASH diet increased LDL peak diameter, whereas the standard DASH reduced the LDL peak diameter. Large LDL size has been associated with a reduced risk of heart disease.
Finding 4: No Increase in LDL-Cholesterol
The higher-fat DASH diet did not increase levels of LDL-cholesterol, compared to the standard DASH diet.
This is inconsistent with studies showing that replacing carbs or unsaturated fats with saturated fats increases LDL-cholesterol.
The authors speculate that the DASH diet may have characteristics that prevent the rise in LDL-cholesterol typically associated with a higher intake of saturated fats.
Bottom Line: The higher-fat DASH diet did not increase LDL-cholesterol, compared to the standard DASH.
This study appears to have been designed and implemented well.
It was a crossover trial, meaning that all participants were on all three diets during different study periods, separated by a 2-week washout period.
The purpose of the washout period was to prevent the previous diet from affecting the results of the next diet.
This washout, however, doesn’t appear to have worked in all cases, since there were some prolonged effects of the higher-fat DASH diet on blood pressure. The reason for this is unexplained.
Other limitations include a small number of participants and a relatively short study period.
Bottom Line: This study did not have any serious limitations. However, the 2-week washout period between diets may not have been long enough with respect to blood pressure.
Summary and Real-Life Application
In short, this study shows that eating slightly more saturated dairy fat while on the DASH diet does not affect its beneficial effects on blood pressure.
Also, it did not have any adverse effects on the blood lipid profile.
A lower-carb, higher-fat DASH diet is a healthy, equally effective option, which may be easier to follow than the standard DASH diet.