Hypertension, or high blood pressure, is a significant global health concern, recognized as the second leading risk factor for disease worldwide, surpassed only by poor diet. Lifestyle modifications, including dietary changes, play a crucial role in managing blood pressure and preventing cardiovascular disease. While recommended dietary guidelines often emphasize the quantity and type of nutrients, conflicting recommendations can confuse individuals. This article explores the relationship between low-carbohydrate diets and high blood pressure, drawing upon observational studies, randomized clinical trials, and mechanistic research to provide a comprehensive overview.
The Role of Carbohydrates in Hypertension
The association between cardiometabolic diseases, including hypertension, and diets high in carbohydrates (particularly refined or high glycemic index carbohydrates) has been documented. However, the role of low-carbohydrate diets remains a subject of debate. Some studies have reported reduced cardiovascular risk with low-carbohydrate diets, while others have found increased risk, especially with long-term follow-up. Interestingly, minimal risk has been observed at around 50% carbohydrate consumption.
Observational studies suggest that the quality of carbohydrates may be more important than the total amount in determining the risk of chronic diseases, including cardiovascular and metabolic diseases. However, specific groups may respond differently to carbohydrate quality and quantity.
A nationwide observational prospective cohort study investigated the relations of the amount and type of carbohydrates with new-onset hypertension in adult Chinese individuals. The results showed a U-shaped association between percentage of dietary carbohydrate intake and new-onset hypertension in adults. These data further support the notion that both high and low percentages of carbohydrate diets are associated with increased risk of hypertension, with minimal risk found at about 50% to 55% carbohydrate consumption. Interestingly, in this study, the increased risks were mainly found in those with lower intake of high-quality carbohydrate or high intake of low-quality carbohydrate. Moreover, an inverse association between the plant-based low-carbohydrate scores for low-quality carbohydrate and new-onset hypertension was also shown. Undoubtedly, these data contribute further to highlight the role of the quality of carbohydrate intake on the development of hypertension and cardiovascular risk, although no direct evidence of mechanisms has been provided.
Randomized clinical trials have shown that higher intakes of dietary fibers, fruits, vegetables, some starches as well as cereals and whole-grain foods may reduce body weight and lower blood cholesterol and systolic blood pressure.
Read also: Safety of Low-Carb Diets During Lactation
Mechanisms of Action
Carbohydrate-containing foods may influence cardiometabolic risk and the development of chronic diseases in various ways according to the type of carbohydrate, and different mechanisms have been hypothesized. Viscous fibers (nonstarch polysaccharide carbohydrate derived from plant) and insoluble fibers (from wheat bran) have shown limited metabolic actions by reducing postprandial glycemia and cholesterol absorption. Moreover, foods containing high-quality carbohydrates (ie, nonstarchy vegetables, whole fruits, legumes, and whole-kernel grains) are effective for the prevention of chronic diseases development including hypertension as they contain also other micronutrients such as antioxidants and antinflammatory molecules which may exert a protective role in the cardiovascular system. Indeed, whole plant foods contain numerous compounds, including vitamins, minerals, antioxidant, and anti-inflammatory phytochemicals, which may interact with each other and exert beneficial actions in the cardiovascular system, possibly by modulating neurohormonal systems and vascular remodeling. In particular, high potassium, antioxidants, and fiber contents in some fruits, vegetables, and grains may contribute to reduce blood pressure levels and to prevent/improve hypertension-related organ damage (ie, coronary heart disease, ischemic stroke).
Hence, the carbohydrate quality seems to have a more important impact on population health as compared to the carbohydrate amount, although further long-term clinical trials and prospective observational research as well as in vitro and in vivo mechanistic studies are required. Indeed, these studies might possibly contribute to further extend the knowledge and clarify the influence of dietary carbohydrates on hypertension risk and the circadian pattern of blood pressure as well as to elucidate the underlying mechanisms including the potential interaction with the intestinal microbiome.
Low-Carbohydrate Diets: Benefits and Risks
Low-carbohydrate diets, such as the ketogenic diet, have gained popularity for their potential to promote weight loss and improve certain metabolic markers. However, their impact on blood pressure and overall cardiovascular health remains a complex issue.
Potential Benefits
Some studies suggest that low-carbohydrate diets may lead to a reduction in blood pressure, particularly in individuals with type 2 diabetes or obesity. A study published in July 2019 showed that following a low carbohydrate diet like the keto diet helped lower blood pressure readings in people with type 2 diabetes. The Norwood diet, based on a recommendation for a substitution of carbohydrates with lower carb alternatives, enabled substantial and sustained improvements in the measured variables of weight, blood pressure and lipid parameters. A low carbohydrate diet may improve both hyperinsulinaemia and insulin resistance, promoting the loss of sodium in the urine so improving blood pressure.
One study found that both the Mediterranean and keto diets can help lower a person’s blood pressure and improve cardiovascular health measurements in people who have obesity or overweight. At the study’s conclusion, researchers found that participants in both diet groups experienced a decrease in blood pressure and weight loss after three months. Scientists also found that participants in both diet groups experienced an increase in their fat-free mass - the total mass of the body excluding fat - and a decrease in their body fat, blood lipid levels, and insulin concentrations.
Read also: Best keto-friendly chips
In a previous small pilot study, it was found that a low carbohydrate diet was associated with significant improvements in blood pressure, weight, ‘deprescribing’ of medications and lipid profiles.
Potential Risks
Despite the potential benefits, concerns exist regarding the long-term effects of low-carbohydrate diets on cardiovascular health. Some studies have linked these diets to increased levels of artery-clogging LDL cholesterol and a potential increased risk of heart disease. The diet's extreme carbohydrate restrictions may lead people to shun most vegetables and fruits and consume large amounts of leafy greens. But the vitamin K in these foods may interfere with the anti-clotting drug warfarin taken by some heart patients.
A study from Li et al5 presents also other few limitations that need to be highlighted and taken into account for future prospective studies. In particular, although most of the related variables (including age, sex, education, body mass index, self-reported diabetes, and cardiovascular diseases) have been included in the regression models, the stratified analysis showed that age did not significantly modify the association between dietary carbohydrate intake and new-onset hypertension, which is possibly due to the fact that only a single group of age (ie, young-adult population) was studied. Moreover, the putative roles of ethnicity and familiarity (ie, genetic predisposition) as well as the effect of carbohydrates on different metabolic variables (including insulin resistance and hyperglycemia which can contribute to hypertension development) were not properly addressed. Hence the effect of age, ethnicity, familiarity, and diet-induced metabolic alterations on hypertension development should be carefully investigated in future prospective studies which should include different ethnic and age groups to evaluate the potential impact of age and racial/ethnic differences on the influence of dietary carbohydrates in hypertension.
Nocturnal Dipping
One study reported that participants following the keto diet had a higher level of “nocturnal dipping” than those in the keto group. Nocturnal dipping refers to the natural decrease in blood pressure that occurs when we sleep. It is a measure of healthy blood pressure regulation, and abnormal nocturnal dipping patterns have been associated with increased risk of heart disease. A 10-20% dip in blood pressure while you sleep is considered normal. Past studies show that not experiencing nocturnal dipping, or the reverse of it, known as nocturnal hypertension, can increase a person’s risk for cardiovascular disease.
Animal Studies
Animal studies have provided insights into the potential mechanisms by which low-carbohydrate diets may affect blood pressure. The spontaneously hypertensive rat (SHR) is a model of evolving hypertension, utilized for understanding the causes of hypertension and the development of more effective strategies for its treatment.
Read also: Best Keto Tortillas
Animal studies indicate that diets high in simple carbohydrates, such as sucrose, can promote hypertension in rodents , whereas consumption of very high-fat diets (≥60% energy from fat) can reduce blood pressure in the SHR.
One study found that SHR fed low-carbohydrate/high-fat diets have lower blood pressure and improved endothelial function of mesenteric arteries. Importantly, systemic glucose homeostasis and insulin-mediated signal transduction in the heart and skeletal muscle were similar between SHR fed low-carbohydrate/high-fat or control diets. Furthermore, mesenteric arterial function was improved in SHR that consumed diets relatively higher in fat content and might contribute, at least in part, to lower blood pressure that was observed in these animals.
Practical Considerations
Given the complexities surrounding low-carbohydrate diets and their impact on blood pressure, it is essential to consider individual factors and consult with healthcare professionals before making significant dietary changes.
Individualized Approach
There’s no ‘one-size-fits-all’ when it comes to dietary patterns. Meeting with a registered dietitian nutritionist (RDN) is recommended to further explore which dietary pattern may be most appropriate for an individual’s needs, current health condition, preferences, goals, genetics and lifestyle. RDNs are trained to bridge the gap between science and everyday life. If you’re looking to manage weight or blood pressure in a way that’s realistic and sustainable, working with an RDN can be a game-changer. It is also important to consider if the specific dietary pattern is sustainable for a long period of time and can be a lifestyle versus a controlled experiment or ‘temporary fix’. Think of dietary patterns like a playlist - the right mix can set the tone for a healthier rhythm in your body and the days ahead.
Focus on Nutrient-Rich Foods
When considering dietary changes to manage blood pressure, prioritize nutrient-rich foods with many health benefits, such as:
- Healthy fats like olives, extra-virgin olive oil, avocados, nuts, and seeds.
- Non-starchy vegetables such as leafy greens, beets, peppers, onions, garlic, scallions, tomatoes, cabbage, and Brussels sprouts.
- Herbs such as chives, basil, mint, rosemary, thyme, and sage.
- Proteins from plants and animals, such as goat cheese, yogurt, beans and lentils, fish, hummus, and tzatziki.
- High fiber foods from whole grains like oats, whole wheat, and rye, and fresh fruits in season such as peaches, plums, apples, grapes, berries, pears, oranges, figs, dates, and cherries.
- Incorporation of green, black, white, or herbal teas.
Long-Term Sustainability
It is important to consider if the specific dietary pattern is sustainable for a long period of time and can be a lifestyle versus a controlled experiment or ‘temporary fix’.
The Norwood Primary Care Study
In 2013 the authors started offering advice on a low carbohydrate diet (defined as <130 g carbs/day) to help people in the Norwood primary care (GP) practice with type 2 diabetes (T2D) and pre-diabetes or impaired glucose tolerance (IGT). In this eight-month pilot study of 19 patients the authors were struck by the significant and unexpected improvements in blood pressure (systolic 148 ± 17 to 133 ± 15 mmHg, p < 0.005; and diastolic 91 ± 8 to 83 ± 11 mmHg, p < 0.05). This occurred despite discontinuing several antihypertensive drugs. The Norwood diet, based on a recommendation for a substitution of carbohydrates with lower carb alternatives, enabled substantial and sustained improvements in the measured variables of weight, blood pressure and lipid parameters.
Methods
A low carb diet was offered as part of routine care by GPs and practice nurses to practice patients with type 2 diabetes (T2D) or impaired glucose tolerance (IGT). Exclusion criteria were end of life patients, pregnancy, eating disorders, being underweight, type 1 diabetes or being under 18 years of age. People with type 2 diabetes on insulin were included (n = 6). Informed consent was obtained. Data was collected from March 2013 to November 2018 during which time we offered patients our study diet programme as part of ordinary appointments. Those who chose to enroll were given our diet sheet and a review appointment a few weeks later to answer practical questions. Further support was offered depended upon patient choice and clinical need. This covered quite a broad spectrum from generally well people with IGT to eighty-year old persons on insulin, reflecting the fact this was part of our day to day work. However, in addition to ‘one to one’ doctor or nurse appointments we offered regular 90 min ‘group sessions’ for up to 30 people at approximately monthly intervals. This included family members, particularly if they did the shopping or cooking.
Our cohort consisted of 154 patients, 90 men and 64 women for whom we had complete data sets for our primary outcomes of blood pressure and weight. Of the 154 participants, 89 were coded as having T2D. This represented 19% of the total practice population with T2D. The age range was 40-89 with a mean of 63 years at the onset of participation (inter-quartile range 53-73 years).
Baseline measurements included the following: Weight, blood pressure, total cholesterol, HDL cholesterol, fasting triglyceride levels and medications for hypertension. We concentrated particularly on advising a dramatic reduction in total dietary sugar, explaining that this involves not just cutting back on table sugar itself but starchy carbohydrates like bread, cereals and potatoes that are themselves made up of glucose (in the form of starch).
Results
The mean time spent on the diet was 24 months (IQR 10-32 months). This was associated with a mean unadjusted reduction of systolic BP of 10.9 mmHg (IQR 0-22 mmHg) (p < 0.0001) and a mean fall in diastolic BP of 6.3 mmHg (IQR 0-12.8 mmHg) (p < 0.0001). The total cholesterol, HDL cholesterol, and fasting serum triglyceride levels are shown in Table 1 and Figure 4. Total cholesterol fell by 0.4 mmol/L (IQR −0.1-0.7), and serum triglyceride by 0.7 mmol/L (IQR 0.1-1.1). An overall sustained reduction of 8% in mean cholesterol and a very large reduction of 32% in mean TG. HDL rose 8% over the duration of the study.
The 154 patients began the study on a total of 163 drugs for hypertension, by the end that had dropped to 128 as there had been a net ‘deprescribing’ of 35 repeat medications, which represented 21.5% of the total.
Discussion
With an average participation of two years our study, it was of long duration compared to many published dietary studies. The effects on blood pressure are particularly interesting. It is likely the improvements underestimate the actual reduction in hypertension burden as 27 patients were able to reduce or discontinue antihypertensive therapy. Their BP at the start could be said to be ‘falsely’ low as they were on medications discontinued by the end of the study. To correct for this we could re-calculate the averages by adjusting the baseline BP to what it was before the medication was started in those 27 individuals. On doing this we arrive at an adjusted BP lowering effect for the cohort of 14.8 mmHg systolic and 8.1 mmHg diastolic. Weight loss alone cannot explain our adjusted drop in blood pressure. Some of the hypertensive patients who responded to the low carbohydrate diet were not even overweight at the beginning. It is possible the physiology of insulin’s action on the kidneys to cause sodium retention holds a clue in cases like these. As mentioned in the introduction, a low carb diet may improve both hyperinsulinaemia and insulin resistance, promoting the loss of sodium in the urine so improving blood pressure. This may explain our (adjusted) average 1.6 mm Hg reduction in systolic blood pressure per 1 kg reduction in weight.