Impact of Nutrition on Urologic and Renal Diseases

Today, physicians and patients are more aware of the relationship between nutrition and disease.  Nutrition is an important part of leading a healthy lifestyle. Combined with physical activity, diet can help patients reach and maintain a healthy weight, reduce their risk of chronic diseases (like heart disease and cancer), and promote their overall health.

Unhealthy eating habits have contributed to the obesity epidemic in the United States. One-third of US adults (33.8%) are obese.¹ Even for people with a healthy weight, a poor diet is associated with major health risks that can cause illness and even death. These include heart disease, hypertension, type 2-diabetes, osteoporosis, and certain types of cancer. Also, good dietary habits and good nutrition are important in the management of various urologic and renal diseases.

As physicians, it is important for us to establish a link between good nutrition and various urologic and renal diseases. This article will emphasize the relationship between diet, nutrition, and management of several urologic and renal diseases. The article will provide evidence-based suggestions that we can provide our patients who have these common conditions.

Overactive bladder (OAB)                                                                       

OAB is a sudden involuntary contraction of the detrusor muscle of the bladder causing urinary urgency, an immediate need to urinate. It is one of the causes of urinary incontinence and affects over 33 million Americans.² Men and women who suffer from OAB often feel embarrassed about their condition and may not seek medical help or bring up their urinary symptoms with their doctors.

OAB symptoms appear to be multifactorial in both etiology and pathophysiology. Symptoms suggest underlying detrusor overactivity, which can be neurogenic, myogenic, or idiopathic in origin. Neurogenic causes of OAB include multiple sclerosis, dementia, Parkinson disease, and diabetic neuropathy. In postmenopausal women, estrogen deficiency can result in OAB symptoms. Estrogen deprivation therapy in younger women with breast cancer has also been associated with increased risk for OAB.

The mainstay of OAB management is anticholinergic medications and beta-3 adrenoceptor agonists. Dietary considerations, however, are also helpful in ameliorating symptoms. Patients with OAB are often sensitive to caffeinated beverages, and consuming caffeine can increase OAB symptoms. One of the treatment recommendations for those who suffer from OAB is to reduce, or better yet, eliminate caffeinated beverages, including coffee, tea and energy drinks, which have significant caffeine content, from their diet. In addition to caffeine serving as a bladder irritant, caffeine is a weak diuretic and increases urine output and contributes to urinary frequency.³

Other dietary culprits include acidic fruit juices such as orange or grapefruit juice, which can alter the pH of urine and exacerbate OAB symptoms. The goal of dietary therapy for OAB can include alkalinizing the urine with 2-4 grams of sodium bicarbonate twice a day. In addition, reducing or eliminating acidic foods such as tomatoes and highly spiced condiments such as chilies and wasabi may also be helpful. Finally, omitting artificial sweeteners such as aspartame and saccharin can also alleviate OAB symptoms.⁴ Patients can consider eliminating carbonated beverages, especially those containing large quantities of caffeine.

A British study indicated a decreased risk of OAB with increased consumption of raw vegetables, which increases dietary fiber content.⁵ Raw vegetables provide up to 30% of dietary fiber. A low fiber diet is associated with constipation and the accompanying straining to defecate. Constipation places increased pressure on the pelvic floor muscles, which are responsible for keeping the urethra closed or coapted. If these pelvic floor muscles become damaged, such as during childbirth, and there is accompanying constipation, then urinary frequency and urgency may occur.

There are a large number of estrogen receptors located in the bladder and the pelvic muscles in women. An estrogen deficiency, as occurs in menopause, results in exacerbation of OAB symptoms. When there is evidence of estrogen deficiency, relief may be achieved with hormone replacement therapy unless the use of estrogen is contraindicated (as in cases of estrogen-positive breast cancer). Clinicians may recommend the use of topical estrogen cream, oral estrogen, or estrogen patches. Topical estrogen such as estradiol vaginal cream every other day or twice a week is effective as an oral hormone replacement therapy for OAB.⁶ In addition, vegetables such as yam and carrots contain phytoestrogens that may supplement the natural estrogens in post-menopausal women and reduce OAB symptoms.⁷

In a longitudinal study of 5000 women over age 40 that focused on various dietary inclusions and OAB onset, higher intake of vitamin D, protein, and potassium were associated with a decreased onset of OAB. There are vitamin D receptors on the detrusor muscle.⁸ Adequate vitamin D allows relaxation of the detrusor and results in a decrease in patients’ urinary urgency.⁹  OAB patients may experience improvement in symptoms with 600 units of vitamin D per day.¹⁰  

The onset and the symptoms of OAB may be associated with smoking. The mechanism linking smoking and OAB symptoms is unclear, but it could be related to an anti-estrogenic hormonal effect on the bladder and urethra and a nicotine-induced contraction of the detrusor muscle.¹¹ Mandhu et al. conducted a retrospective study with more than 11,000 women and found that smoking was associated with a 14% increased risk of OAB symptoms.¹² Thus, in addition to dietary modifications, smoking cessation is advised for patients with OAB.

Perhaps one of the least expensive yet effective treatments of OAB is fluid restriction. Callan et al. demonstrated that increasing fluid by 25% to 50% could increase daytime frequency; however, the study did not show a significant effect on urgency. Increasing fluid intake is associated with worsening of OAB symptoms in observational studies.¹³ Mild to moderate fluid restriction, however, results in significant improvement in OAB symptoms, especially nocturia. 

Nocturia is one of the most distressing symptoms of OAB which is also amenable to fluid restriction. In a study, investigators managed nocturia using fluid restriction after 6 pm.  Participants who completed behavioral treatment that included fluid restriction demonstrated a reduction in mean number of voids per day from 11.3 in baseline to 9.1 after treatment. This decrease of 2.2 voids per day (18.8%) was statistically significant (P < .001).¹⁴

Interstitial cystitis (IC)

IC or chronic pelvic pain syndrome (CPPS) consists of pelvic pain and a persistent desire to urinate accompanied by urinary frequency, nocturia, and voiding small volumes of urine. The hallmark of IC is the presence of these urinary symptoms with a negative urine culture. IC affects about 700,000 to 1 million Americans, with 90% of patients being women.¹⁵ This incidence is probably underreported. Many patients may be misdiagnosed as having cystitis or prostatitis, as these conditions share similar lower urinary tract symptoms. Possible causes of IC include defects in the lining of the urinary bladder that cause irritation, bladder trauma, pelvic floor muscle dysfunction, autoimmune disorders, neurogenic inflammation, spinal cord trauma, genetics, or allergy.

Patients with IC are advised to avoid bladder irritants such as citrus food and caffeinated beverages for the same reason that caffeine is to be avoided in patients with OAB. A study by Shorter et al identified foods and beverages that worsened the symptoms of IC. In this study, a questionnaire was administered to 124 patients with IC. The questionnaire asked patients to indicate whether the foods and beverages listed improved, worsened, or had no effect on their symptoms. The most frequently reported foods and fluids that exacerbated their symptoms were coffee, tea, soft drinks, alcoholic beverages, hot peppers, critic fruits and juices, and artificial sweeteners.¹⁶

Sonmez et al reported that a combination of both calcium glycerophosphate and sodium bicarbonate improved IC symptoms.¹⁷ In another study by Shorter et al, patients were asked to take 2 tablets (0.66 grams) of calcium glycerophosphate over a 4-week period. Patients reported improvement in their symptoms, with a decrease in urgency and dysuria. In addition, these patients also reported a reduction in IC exacerbations, especially from foods such as pizza, spicy food, chocolate and alcohol.¹⁸

It is important to mention that there is a significant placebo effect in the management of IC patients. Patients with moderate to severe IC have experienced significant improvement after receiving only advice and support from their physicians. Supportive therapy is risk free, inexpensive, and without side effects. Consequently, proving efficacy of any of the treatments for IC with rigorous placebo-controlled trials is difficult due to a significant effect of the placebo intervention.¹⁹

Certainly, medications are available for treating IC, such as pentosan polysulfate sodium and DMSO. Diet modification, however, can supplement pharmacotherapy. Patients should be provided with a dietary list of bladder irritants (Figure 1). Since the list of bladder irritants is extensive, and in order to identify which dietary culprits are responsible for symptoms of IC, it is initially advisable to eliminate all possible bladder irritants for 5-7 days and then start adding potential irritants to the diet, thus enabling identification of the offending foods or fluids that might exacerbate the symptoms.

Prostatitis

Prostatitis is one of the more common conditions seen in a urologic practice. Although an extensive review of this condition is beyond the scope of this paper, prostatitis, an inflammation of the prostate gland presents as acute or chronic, bacterial or non-bacterial. Non-bacterial, chronic prostatitis is the most common variety. Symptoms include generalized sense of discomfort in the pelvis, and with urination, along with frequency, urgency, pressure sensation, and occasionally low-grade fever

The US prevalence of prostatitis is approximately 8.2%. Prostatitis accounts for about 8% of all urologic visits.²⁰ There is a relationship between diet and urinary symptoms associated with chronic prostatitis.  Patients with chronic prostatitis may consider avoiding foods and beverages known to exacerbate urinary symptoms. These foods may include spices, hot peppers, alcohol, wheat, and gluten.²¹ Men find wheat-free or gluten-free diets to be the most beneficial in managing their prostatitis symptoms.²² Furthermore, drinking ample quantities of water and consuming foods high in fiber and zinc may reduce the symptoms of chronic prostatitis. Also, herbal tea or caffeine-free-tea can be beneficial for controlling chronic prostatitis.²²

Goodarzi et. al found that zinc supplementation helps patients with chronic prostatitis in relieving their symptoms. The conducted a study that included 123 patients aged 18-40 years diagnosed with chronic prostatitis.²³ All patients completed a chronic prostatitis symptom index questionnaire and a pain score questionnaire before entering the study. Each patient was given  220 mg/day of zinc sulfate while a control group was given a placebo. At the end of 12 weeks, the zinc sulfate group had a reduction in prostatitis symptom index score and pain score compared with the control arm. The effectiveness of zinc can possibly be attributed to its anti-bacterial and immunomodulatory functions.²³ Zinc is a prominent chemical in seminal fluid but its precise role in the management of prostatitis remains unclear. Supplementation with oral zinc appears to be a simple, safe and a potentially effective option for these men.

Benign prostatic hyperplasia 

Benign prostatic hyperplasia (BPH) affects approximately 19 million men in the United States, but only about 3 million seek treatment.²⁴ Symptoms include a decrease in the force and caliber of the urine stream, frequency of urination, urgency to void, a feeling of not emptying the bladder, nocturia, and post-micturition dribbling. The incidence of BPH increases with age. Only about 10% of men in their 30s exhibit these lower urinary tract symptoms (LUTS). The incidence increases to 60% among men in their 60s. Nearly all men over 70 will have some degree of LUTS.²⁵ By controlling their diet, many patients with BPH can significantly improve their urinary symptoms. Benign prostate enlargement is largely driven by the conversion of testosterone to dihydrotestosterone. It is not known if any foods affect testosterone directly, but there is strong evidence that a plant-based diet consisting of beans, peas, lentils, vegetables, and sesame seeds—essentially a Mediterranean diet—can be helpful in men with LUTS and in decreasing the risk of developing LUTS.  El Jalby et. al, in their extensive literature review on this subject, found 1325 citations and ultimately selected 35 studies for their review. Although dietary studies have some built-in challenges, the studies essentially revealed the above findings with regards to diet and LUTS, in addition to salutary effects on erectile dysfunction.²⁶ 

Nephrolithiasis

Approximately 9% of the US population is affected by nephrolithiasis.²⁷ There are 4 major types of nephrolithiasis: calcium, uric, struvite, and cystine. Dietary modifications may help prevent recurrent nephrolithiasis, and those modifications depend on the type of kidney stone. For example, uric acid stone formers should decrease intake of red meat and shellfish because these foods contain high concentration of purines which are metabolized into uric acid.²⁸ Increased purine intake may lead to a higher production of uric acid, which aggregate as crystals in the collecting system of the kidneys. Patients are advised to review information readily available listing foods high in purines and be cautious in their dietary intake of these foods. Patients with uric acid kidney stones should follow a diet that consists of fruits, vegetables, and whole grains, and limit their alcohol intake.

Patients with calcium oxalate stones, the most common type, should avoid foods high in oxalate such as spinach, nuts, and wheat bran.²⁹ Oxalate is also found in certain fruits and vegetables, such as rhubarb, beet and potatoes. Patients with calcium stones are often advised to avoid foods high in calcium, such as dairy products.

Although excessive calcium intake is not recommended, either dietary or supplemental calcium remains important. Calcium restriction does not inhibit the development of calcium oxalate stones, but it does have a negative effect on bone health, especially in women who are more prone to osteopenia and osteoporosis.

Patients with calcium phosphate nephrolithiasis should limit their sodium intake because excess sodium leads to an increase loss of calcium in the urine. With sodium restriction, there is a relative decrease in circulating blood volume. The result is increased reabsorption of sodium, water, as well as calcium at the level of the proximal convoluted tubule, thereby decreasing urinary calcium excretion. Foods containing large quantities of sodium include salted or canned meat, fish, and poultry, as well as pizza and nuts, buttermilk, olives, and pickles.³⁰ In addition, patients with calcium phosphate stones should also limit their intake of oxalate-rich foods.

Patients with cystine stones should restrict consumption of meat and other animal proteins and salt intake. They also should be advised to consume more fruits and vegetables because these foods make the urine less acidic and decrease the excretion of cystine.³¹

The time-honored method of prevention for all kidney stones is adequate intake of fluids, especially water. All patients with nephrolithiasis should consume at least 2.5 liters of fluid per day. Patients with cystine stones are advised to consume 4 liters of fluid per day.³¹

Increased fluid intake is recommended for patients in environments with low humidity and who lose water through via perspiration and chronic diarrhea.

Erectile dysfunction (ED)

A study of data from the National Health and Nutrition Examination Survey (NHANES) found that the US prevalence of ED in men aged over 20 years was 18.4%, or about 18 million men. Not only is ED is strongly associated with age but also in men with diabetes, hypertension, and a history of cardiovascular disease.³²  

Since ED is correlated with hypertension, it is important to maintain a heart-healthy diet. A study of 555 men with type 2 diabetes demonstrated that patients who followed a Mediterranean diet, which is high in fruits, vegetables, nuts, and whole grains and low in red meat, had a decreased prevalence of ED and were more likely to be sexually active than men who did not follow the Mediterranean diet.³³

Excessive salt intake can result in hypertension and atherosclerosis, which can narrow the lumen of arteries and decease blood flow not only to the coronary arteries but also to the penis, making erection difficult or impossible. Therefore, patients with ED should be advised to restrict foods high in salt content such as bacon, ham, smoked meat, potato chips, and crackers.

A systematic review by Gandaglia et al. showed that ED often precedes cardiovascular disease (CVD). Consequently, ED can be used as an early marker to identify men who are at a higher risk for CVD events.³⁴ It is important to note that ED may precede a diagnosis of CVD by as many as 5 years.³⁵ The explanation of ED preceding CVD is that the diameter of the penile arterial blood supply is normally one-third the size of the coronary arteries. As a result, symptoms of ED secondary to hypertension and hypercholesterolemia may occur before symptoms of coronary disease, ie, angina or myocardial infarction. Therefore, if a patient has ED, particularly at a young age, a clinician may consider a referral to a cardiologist to access occult CVD.

Chronic kidney disease (CKD)

CKD affects approximately 31 million Americans, and most CKD cases are undiagnosed because it may be asymptomatic in early stages.³⁶ Type 1 and type 2 diabetes and high blood pressure are the most common causes of CKD.³⁷ The 4 substances that patients with CKD need to restrict or avoid are sodium, phosphorus, calcium, and potassium. Excessive sodium impacts blood pressure and water balance. CKD and excessive sodium consumption results in a worsening of hypertension. This can be controlled by avoiding foods high in salt such as soy sauce, teriyaki sauce, canned foods, processed foods, and snacks with high sodium content. Patients with CKD should limit their sodium to 2000 mg per day.

As kidney function decreases, phosphorus excretion by the kidneys decreases and calcium is not absorbed from gastrointestinal tract, leading to low blood levels of calcium. In response to a decrease in calcium, parathyroid hormone (PTH) production increases and results in the loss of calcium and phosphorus from bones, which can lead to osteoporosis. The increase of phosphorus and calcium in the blood stream can cause vascular calcifications and worsening arteriosclerosis.³⁸

Patients with CKD are advised to restrict dietary phosphorus to less than 800-1,000 mg per day.  Foods high in phosphorus to avoid or decrease include milk, ice cream cheese, yogurt, chocolate, and legumes.

Patients with CKD should also avoid excessive quantities of protein, including meat, nuts, and dried beans. Accumulation of excess protein damages glomerular structure, leading to or aggravating CKD. A low-protein diet (0.6-0.8 g/kg/day) is recommended for patients with CKD.³⁹

Patients with CKD need to be concerned about their potassium level, as hyperkalemia can result in arrhythmias. Potassium can be regulated by reducing consumption of bananas, melons, milk, and yogurt, as well as poultry and pork. Patients with CKD disease should limit potassium intake to 2000 mg per day.

Fluid restriction may be required in patients with CKD, especially those patients with end-stage kidney disease (ESKD) who are on dialysis. Dialysis patients may need to limit fluids between dialysis treatments. Because patients with ESKD have diminished urine output, excessive fluid expands the extracellular fluid space and results in peripheral edema, weight gain, hypertension, and congestive heart failure.

Bladder Cancer and diet

In 2017, approximately 80,000 adults were diagnosed with bladder cancer in the United States. Worldwide more than 400,000 cases are diagnosed yearly, making it the seventh most common form of cancer.⁴⁰ Men are four times more likely to be diagnosed with the malignancy than women, especially white men whose incidence rates are double those of black men. Bladder cancer mostly affects older people, with an average age at diagnosis of 73 years.⁴¹

Although tobacco use is the single biggest risk factor for bladder cancer, dietary components may alter the natural history of bladder cancer and even reduce the risk of recurrence or progression.

Increased intake of cruciferous vegetables such as broccoli sprouts, kale, and cabbage is associated with a decreased risk of bladder cancer. Cruciferous vegetables contain isothiocynates, which are known to induce anticarcinogenic effects through phase-2 cytoprotective enzymes.⁴² Evidence also suggests that tea consumption may decrease the risk for bladder cancer. Drinking water contaminated with arsenic—which is an issue in some places—is risk factor for bladder cancer.⁴³  

A large international trial, the BLEND study, is attempting to address the issue of diet and bladder cancer in a prospective manner. Results of this trial should be forthcoming in the near future.⁴⁴

Conclusion

Diet and supplements impact numerous urologic conditions. Although the exact pathophysiology regarding these relationships is not apparent in all cases, it is prudent for healthcare providers to be aware of the relationships and counsel patients regarding proper diet for their particular urologic problem. There clearly are benefits and risks associated with certain foods as they pertain to the urologic problems discussed in this review, but in many respects, patients who consume a prudent diet such as the Mediterranean, the MIND, or the DASH diet can decrease the risks for these diseases or help control their symptoms, in addition to enhancing their overall health.

*David F. Mobley, MD, is Associate Professor in Clinical Urology at the Houston Methodist Academic Institute. **Hevin Patel is a pharmacologist at Tulane University in New Orleans. ***Neil Baum, MD, is Professor of Clinical Urology at Tulane University in New Orleans.

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