High blood pressure and type 2 diabetes often occur together, especially in people who are overweight.
Having both conditions can greatly increase the risk of heart disease, stroke, kidney problems and other serious health complications.
Prediabetes is also important because blood sugar is already higher than normal, although it has not yet reached the level used to diagnose diabetes.
Food choices can help manage all of these conditions, but there is continuing debate about which eating pattern works best. A study published in The Annals of Family Medicine directly compared two very different approaches: the DASH diet and a very low-carbohydrate diet. The results suggest that sharply reducing carbohydrates may provide larger short-term improvements for some people.
The DASH diet was originally designed to help lower blood pressure. Its name stands for Dietary Approaches to Stop Hypertension. It generally encourages vegetables, fruits, whole grains, beans, nuts and low-fat dairy while limiting excess salt, sugary foods and foods high in unhealthy fats.
A very low-carbohydrate diet takes a different approach. It greatly limits foods that contain large amounts of carbohydrates, including many breads, pasta, rice and sugary foods. The diet usually contains more fat and protein, and carbohydrate intake may be low enough for the body to begin relying more heavily on fat for energy.
Researchers recruited 94 adults who had high blood pressure and either prediabetes or type 2 diabetes. Every participant was also overweight or obese. The participants were randomly assigned to follow either the DASH diet or a very low-carbohydrate eating plan for four months.
The study also examined whether extra behavioral support would improve results. Some participants received additional help involving cooking, mindful eating, emotional awareness and other strategies intended to make dietary changes easier. Others followed their assigned diet without this added program.
After four months, the very low-carbohydrate group showed larger improvements in several important measures. Their systolic blood pressure, the upper number in a blood pressure reading, fell more than it did in the DASH group. Their blood sugar control and body weight also improved more.
These changes are important because high blood pressure and high blood sugar can gradually damage blood vessels and organs. Losing excess weight can also improve the body’s response to insulin and reduce the strain placed on the cardiovascular system. Improving several risk factors at the same time could therefore have meaningful health benefits.
The researchers also found that the additional support program did not produce clear extra improvements in the main outcomes. This does not necessarily mean that cooking skills, emotional support or mindful eating are useless. The study may simply have been too small or too short to detect their full effects.
The findings add to evidence that carbohydrate restriction can improve blood sugar and weight in some people with metabolic health problems. When fewer carbohydrates are eaten, the body generally has less glucose entering the bloodstream after meals. Weight loss itself can then provide additional benefits for blood pressure and diabetes control.
However, the study does not establish that a very low-carbohydrate diet is the best choice for everyone. Only 94 people took part, and the trial lasted four months. A diet that produces strong results over several months may be difficult for some people to maintain for several years.
Long-term health effects also matter. Researchers need to know whether improvements in blood pressure, blood sugar and weight continue and whether the diet affects cholesterol, kidney health, heart disease and other outcomes over time. The quality of foods chosen within a low-carbohydrate diet may also make an important difference.
For example, a low-carbohydrate diet based mainly on vegetables, nuts, seeds, fish and other nutritious foods is very different from one dominated by highly processed meat and foods rich in saturated fat. Similarly, the DASH diet can vary depending on the foods a person actually chooses. A diet’s name alone does not tell the whole story.
People taking medicines for diabetes or high blood pressure should be particularly careful when making major dietary changes. A large reduction in carbohydrates or body weight can change blood sugar and blood pressure quickly, which may affect the amount of medication needed. Medical supervision can help prevent blood sugar or blood pressure from falling too low.
The study’s randomized design is an important strength because assigning participants to different diets helps reduce some of the differences that can confuse observational nutrition research. At the same time, the small sample and short follow-up mean the results should be considered promising rather than final. Larger trials are needed to determine whether the advantage continues over the long term.
Overall, the study published in The Annals of Family Medicine suggests that a very low-carbohydrate diet may produce greater short-term improvements in blood pressure, blood sugar and weight than the DASH diet in adults who have several metabolic health problems.
The findings offer another possible dietary option, but the best approach will depend on a person’s health, preferences and ability to maintain the eating pattern safely over time.
If you care about nutrition, please read studies about the harm of vitamin D deficiency, and Mediterranean diet may preserve brain volume in older adults.
For more health information, please see recent studies about foods to naturally lower high blood pressure, and a simple breakfast switch can help control type 2 diabetes.
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