Diet rich in fruits and vegetables may reduce heart and kidney disease risk

• Uncontrolled high blood pressure can cause complications such as chronic kidney disease and increase the risk of death due to cardiovascular diseases.
• Lifestyle modifications, such as adopting a diet rich in fruits and vegetables, and drug therapy are effective in managing high blood pressure.
• A new study shows that increased consumption of fruits and vegetables in combination with conventional drug therapy was more effective than drug therapy alone in preserving kidney health and improving cardiovascular health in high blood pressure patients with chronic kidney disease.

Hypertension, commonly known as high blood pressure, is the leading preventable risk factor for cardiovascular disease, such as heart disease and stroke. Based on 2017-2020 data, 47% of U.S. adults are estimated to have hypertension.

Uncontrolled high blood pressure can also lead to the occurrence and progression of chronic kidney disease . The early adoption of lifestyle modifications, such as dietary changes, can reduce the risk of complications of uncontrolled hypertension and the need for drug therapy. However, such dietary interventions are often under-utilized.

A new 5-year follow-up study published in The American Journal of Medicine involving high blood pressure patients with chronic kidney disease shows that incorporating 2 to 4 additional cups of fruits and vegetables in their daily diet along with drug therapy resulted in lower blood pressure, a larger reduction in cardiovascular risk factors, and a greater preservation of kidney health than drug therapy alone.

The patients were specifically prescribed fruits and vegetables that increase blood pH levels after their metabolism. The protective effects on kidney health in the group consuming the diet rich in fruits and vegetables were also seen in participants who were administered an oral sodium bicarbonate tablet daily.

Sodium bicarbonate also increases the blood pH, and these results suggest that rebalancing of plasma pH could have potentially mediated the effects of increased fruit and vegetable consumption on kidney health.

However, while both were shown to improve kidney health, only consuming fruits and vegetables, and not sodium bicarbonate, reduced blood pressure and improved cardiovascular disease risk factors.

The study’s author, Dr. Donald Wesson , a professor of internal medicine at The University of Texas at Austin, said, “The study supports redoubling our efforts to make diets high in fruits and vegetables foundational to the treatment of hypertension, with drugs added as needed to achieve blood pressure goals and to prevent kidney and cardiovascular complications.”

“An additional benefit of including extra fruits and vegetables in hypertension management appears to be that lower doses of anti-hypertensive drugs will be needed to achieve these health benefits,” said Dr. Wesson.

Link between hypertension and chronic kidney disease

Besides cardiovascular diseases , uncontrolled high blood pressure is also a risk factor for chronic kidney disease. High blood pressure is associated with the narrowing and stiffening of blood vessels in the body, including the kidneys.

While the body possesses mechanisms to limit kidney damage in response to changes in systemic blood pressure, once blood pressure increases beyond a certain threshold, it can cause the blood vessels in the kidney to harden and influence their function.

Specifically, prolonged high blood pressure can cause damage to the glomeruli, the specialized blood vessels in the kidney that filter wastes and water from the blood. High blood pressure can thus impair kidney function, hampering its ability to filter wastes from the blood. In addition, chronic kidney disease is also characterized by the excretion of proteins in the urine.

The progression of chronic kidney disease further increases the risk of cardiovascular disease, with cardiovascular disease being the leading cause of death in patients with kidney disease. This highlights the importance of the management of high blood pressure and protecting kidney function.

Role of diet in managing hypertension

Lifestyle changes, including adopting healthier dietary patterns, are the recommended first line of treatment for managing high blood pressure . For instance, the Dietary Approaches to Stop Hypertension (DASH) diet, promoting the consumption of fruits, vegetables, lean protein, and low-fat dairy products, has been developed to help lower blood pressure in patients with hypertension.

Moreover, the DASH diet can reduce overall cardiovascular disease risk and prevent or slow down the progression of chronic kidney disease. In addition, medications, such as angiotensin receptor blockers , are typically prescribed to patients with high blood pressure and other conditions like chronic kidney disease or heart failure.

In general, studies suggest that diets rich in fruits and vegetables, such as the DASH diet, are linked to a reduced risk of chronic kidney disease occurrence and progression and lower cardiovascular disease risk.

In the present study, the researchers further examined the protective role of fruits and vegetables in individuals with hypertension and chronic kidney disease.

How acid-producing foods affect kidney health

Most plant-based foods, including fruits and vegetables, produce basic (alkaline) compounds after digestion, leading to a net increase in blood pH levels. So, these foods are referred to as alkaline foods.

In contrast, most animal products and grains, consumed in large amounts in Western diets, tend to produce acid and decrease blood pH levels after their metabolism. These are referred to as acidic foods.

The kidneys contribute to the maintenance of blood pH levels by excreting acids and reabsorbing bases. However, the kidneys can only excrete a limited amount of acid to maintain the body’s pH, and the higher consumption of acid-producing foods can potentially impair kidney function.

“Our animal studies showed years ago that mechanisms used by kidneys to remove acid from the blood can cause kidney injury if the animals were chronically exposed to an acid-producing diet. Our patient studies showed similar findings: that is, an acid-producing diet (one high in animal products) was kidney-harmful, and one that is base-producing (one high in fruits and vegetables) is kidney-healthy,” explained Dr. Wesson.

Observational studies also suggest that consuming a diet rich in acidic food is associated with negative health outcomes , including increased risk of cardiovascular diseases.

“Other investigators showed that a diet high in fruits and vegetables is heart-healthy. We hypothesized that one way that fruits and vegetables are both kidney- and heart-healthy is that they reduce the amount of acid in the diet and therefore the amount of acid that kidneys have to remove from the body,” Dr. Wesson further noted.

Consistent with this hypothesis, some studies have suggested that dietary acid reduction using oral sodium bicarbonate (baking soda) can slow down the progression of chronic kidney disease . However, more research is needed to better understand the role of dietary acid load in preventing and managing chronic kidney disease.

In the present study, the researchers compared the effectiveness of increased consumption of fruits and vegetables with sodium bicarbonate in slowing the progression of chronic kidney disease, controlling blood pressure, and improving cardiovascular health in high blood pressure patients with established kidney disease.

2 to 4 cups of fruit a day

The present randomized controlled study involved 153 individuals with high blood pressure and chronic kidney disease. The study only included participants with an elevated urine albumin-to- creatinine ratio (200mg/g).

Albumin is a protein present in blood, whereas creatinine is a byproduct of muscle metabolism that is normally excreted via the urine. High levels of albumin in the urine can indicate chronic kidney disease, and these patients are at an increased risk of cardiovascular diseases and further progression of kidney disease.

Although these patients had kidney disease, they still showed normal glomerular filtration rates , placing them in a category likely to benefit the most from kidney-protective interventions. The participants were randomly assigned to either the fruits and vegetables intervention, oral sodium bicarbonate treatment, or the usual treatment groups.

The participants in the fruits and vegetables group consumed 2 to 4 additional cups of base-producing fruits and vegetables daily, in addition to their regular daily diet. Individuals in the sodium bicarbonate group were given an oral dose that would have a similar effect on blood pH levels to that observed after the digestion of 2 to 4 cups of fruits and vegetables.

All participants received usual care, which involved statins to protect cardiovascular health and anti-angiotensin II blockers to preserve kidney health. The patients were tracked over a period of five years to assess changes in kidney and cardiovascular health.

Health impact of eating more fruits and vegetables

During the five-year follow-up period, the researchers tracked changes in glomerular filtration rates to assess kidney function and in urine albumin-to-creatinine ratio to monitor kidney disease progression. They also looked at cardiovascular disease markers.

The researchers found that the individuals in the usual treatment group showed a greater decline in kidney function and a larger increase in the urine albumin-to-creatinine ratio than both the fruits and vegetables and sodium bicarbonate intervention groups.

The researchers did not observe a difference in kidney function or urine albumin levels between the fruits and vegetables intervention and sodium bicarbonate group. These results suggest that both increased consumption of fruits and vegetables, as well as oral sodium bicarbonate intake, had a greater protective effect on kidney health and function than drug therapy alone.

Moreover, both the fruits and vegetables intervention and the sodium bicarbonate groups showed higher plasma bicarbonate levels than the usual treatment group, which may indicate better acid-base balance in the body. This suggests that both increased fruit and vegetable consumption and oral sodium bicarbonate could potentially exert protective effects on kidney health through changes in the acid-base balance.

Participants in all three groups showed a decline in systolic blood pressure during the follow-up period, but the fruits and vegetables intervention group showed the largest reduction. In addition, the fruits and vegetables intervention group showed greater improvements in other cardiovascular markers, including body mass index and low-density lipoprotein (LDL) cholesterol, than the oral sodium bicarbonate and usual treatment groups.

Lastly, participants in the fruits and vegetables intervention group had superior health outcomes despite being on lower doses of blood pressure medication than the sodium bicarbonate and usual treatment groups.

“ This study demonstrated that a diet high in fruits and vegetables can significantly lower important indices of cardiovascular disease risk such as high blood pressure, LDL cholesterol, and BMI. These results further support our recommendations to eat a diet rich in fruits and vegetables as part of a ‘heart-healthy diet.’”
— Dr. Cheng-Han Chen, MD , a board-certified interventional cardiologist and medical director of the Structural Heart Program at MemorialCare Saddleback Medical Center in Laguna Hills, CA