Unlock the Power of the Mediterranean Diet to Transform Kidney Disease Health!

Chronic kidney disease (CKD) has emerged as a significant public health concern, often intertwined with other health issues such as hypertension, diabetes mellitus (DM), and obesity. The Mediterranean diet (MD), known for its potential to reduce the risk of cardiovascular disease and cancer, and its ability to promote weight loss in obese individuals, has garnered attention as a dietary approach for patients with CKD. This article aims to provide a comprehensive overview of the Mediterranean diet and its adaptations for individuals with CKD, considering the various stages of the disease.

Introduction

CKD is characterized by the progressive deterioration of the glomerular filtration rate, with aging, hypertension, and diabetes mellitus being the primary causes. Recent studies have also highlighted the association between obesity and the worsening of CKD, identifying it as a major factor in the development of new-onset CKD. Moreover, high protein intake has been linked to glomerular hyperfiltration and increased intraglomerular pressure, potentially exacerbating CKD progression.

The Mediterranean diet, a traditional dietary pattern rich in plant-based foods, has been extensively studied for its potential health benefits. It has been suggested that the MD can reduce the risk of cardiovascular disease and cancer, and may also offer protection against type 2 diabetes mellitus.

Defining the Mediterranean Diet

The Mediterranean diet is characterized by a high intake of plant-based foods, including cereals, legumes, nuts, fruits, vegetables, and herbs. It is low in red meat and includes a moderate intake of fish, seafood, eggs, white meat, and dairy products. Alcohol consumption, primarily wine, is moderate and typically consumed during meals where culturally acceptable. Extra virgin olive oil serves as the principal source of fat, added generously to vegetables and legumes.

Key components of the Mediterranean diet include:

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High consumption of vegetable products: Emphasizing fruits, legumes, mushrooms, and whole-grain cereals, with fruits often consumed as desserts or snacks.
Seasonal and local foods: Prioritizing the consumption of seasonal and locally sourced foods for sustainability.
Plant-based protein sources: Favoring plant-based protein sources such as legumes, alongside animal protein sources low in saturated fats.
Fish consumption: Consuming fish, particularly those rich in omega-3 fatty acids, two to three times per week. Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids found in fish are known to reduce the risk of coronary heart disease and possess anti-inflammatory properties.
Moderate wine consumption: Consuming wine in low to moderate amounts during meals.
Portion control: Practicing frugality and moderation in portion sizes, aligning with the energy needs of modern lifestyles.
Hydration: Maintaining adequate daily hydration, primarily through water and unsweetened beverages.
Balanced meals: Combining cereals, vegetables, and fruits in main meals consumed daily, with a minimum of three servings per week.

Benefits of the Mediterranean Diet

Numerous studies have demonstrated the beneficial effects of the Mediterranean diet on various health outcomes. These include:

Reduced risk of cardiovascular disease and cancer.
Potential protection against type 2 diabetes mellitus.
Inverse relationship with metabolic syndrome.
Improved lipid control.
Reduced blood pressure.
Lower acid load.
Improved gut microbiota.
Decreased inflammation.
Amelioration of constipation.

Mediterranean Diet and CKD

The Mediterranean diet has garnered attention as a potential dietary approach for patients with CKD due to its positive influence on endothelial function, inflammation, lipid profile, and blood pressure. Several studies have explored the relationship between the Mediterranean diet and CKD, with promising results.

A systematic review and meta-analysis by Bash et al. concluded that a healthy diet pattern, possibly resembling the Mediterranean diet, characterized by high consumption of fruits, vegetables, nuts, legumes, and whole grains, and low consumption of salt, sugary drinks, and meat, was associated with a lower incidence of CKD and albuminuria.

The 2020 KDOQI guidelines suggest the Mediterranean diet in adults with CKD stages 1-5 not on dialysis and in transplant patients to improve lipid control. In CKD stages 1-4 patients, an increase in fruit and vegetable consumption is recommended to reduce body weight, blood pressure, and acid load production.

Adapting the Mediterranean Diet for CKD Patients

While the Mediterranean diet offers numerous health benefits, adapting it for CKD patients requires careful consideration of specific nutritional needs and restrictions. Principal nutritional problems in CKD are related to potassium, phosphorus, and sodium intake. The classic guidelines in CKD restricted the consumption of vegetable and whole grain products due to their high levels of potassium and phosphorus. However, current publications recommend increasing their intake because it is not related to serum potassium levels increase.

General Recommendations

Protein Intake: The KDOQI guidelines recommend a low-protein diet that provides 0.55-0.6 g/kg/day for patients with CKD stages 3-5 not on dialysis who are metabolically stable, or a very low-protein diet that provides 0.28-0.43 g/kg/day plus the use of ketoanalogues. For the earlier stages (1-3) of the disease, some guidelines suggest the use of moderately low-protein diets of 0.8-1 g protein/kg bodyweight/day.
Energy Intake: The latest KDOQI guidelines recommend an energy intake of 25-35 kcal/kg body weight/day to maintain an adequate nutritional status, considering age, gender, physical activity level, body composition, weight goals, CKD stage, and presence of concurrent disease or inflammation. In hypercatabolic patients, an energy intake of 30-35 kcal/kg/day is recommended.
Potassium and Phosphorus: The KDOQI guidelines do not recommend phosphorus and potassium intake restriction, unless the biochemical blood values are altered.

Practical Adaptations

Potassium Reduction: Employ cooking methods to decrease potassium levels in vegetable foods.
Phosphorus Control: If phosphorus levels are elevated, focus on the phosphorus/protein ratio of foods. It is recommended to consume foods with a phosphorus/protein ratio lower than 12 mg/g and limit the intake of foods with a ratio higher than 16 mg/g.
Sodium Restriction: Moderate the consumption of common salt while retaining tools to flavor dishes, such as spices.
Serving Sizes: Carefully consider the amount of potassium per portion of food served and the potassium/fiber ratio. Restrict foods with a high potassium content that cannot be subjected to culinary techniques to reduce it.
Protein Sources: To reach protein requirements without decreasing energy intake, consider the serving of protein foods, especially animal products (meat, fish, eggs, and dairy products).

Stage-Specific Recommendations

CKD Stages 3-5 (Not on Dialysis): A low-protein diet (0.55-0.6 g/kg/day) is recommended for metabolically stable patients.
CKD Stages 1-3: Moderately low-protein diets of 0.8-1 g protein/kg bodyweight/day may be considered.
Hemodialysis and Peritoneal Dialysis: Current guidelines recommend that metabolically stable adults with CKD stage 5 on hemodialysis or peritoneal dialysis have a protein intake of 1-1.2 g/kg/day to maintain an adequate nutritional status. Some guidelines recommend a protein intake higher than 1.2 g/kg/day, increasing to 1.5 g/kg/day in case of peritonitis. An energy intake of 25-35 kcal/kg/day is recommended to minimize protein catabolism.
Kidney Transplantation: A subsequent consensus document recommends a moderate protein intake of 0.8-1 g/kg/day. In case of proteinuria or a GFR of <45 mL/min/1.73 m2, a 0.6-0.8 g/kg/day intake is recommendable, with at least 50% of the high biological value proteins. The KDOQI guidelines recommend the MD pattern in these patients without adaptations.

The Mediterranean Renal Diet

The Mediterranean Renal Diet (MedRen diet) is an adaptation of the Mediterranean diet that includes quantitative limitations of sodium, protein, and phosphate intake. This approach involves:

Reducing meat consumption.
Increasing consumption of plant-based proteins.
Ensuring a high intake of fibers, vitamins, alkali, and polyphenols.
Using extra virgin olive oil.

The MedRen diet can be implemented easily in mild-to-moderate stages of CKD with good results, both in terms of adherence to prescriptions and metabolic compensation.

Key Considerations for the MedRen Diet

Plant-Based Proteins: Encourage more frequent consumption of plant-based protein, favoring the use of a combination of cereals and legumes several times a week instead of meat and fish and other sources of animal protein.
Legume Preparation: Recommend soaking and boiling legumes and discarding the cooking water to reduce potassium and phosphate content.
Nuts: Limit nut consumption due to their high content of phosphate and potassium.
Serving Sizes: Establish adequate serving sizes for each patient, particularly regarding foods rich in proteins, salt, and phosphorus.

Gut Microbiota and the Mediterranean Diet in CKD

Dietary changes are known to affect gut microbiota metabolism and composition. The benefits of MD can also be transferred to CKD population. Adequate manipulation of food intake in CKD may reduce the uremic toxins typically produced by gut microbiota that potentially increased the risk of cardiovascular and kidney damage. Fiber intake, provided by plant-based foods, promotes positive microbiota composition and metabolism, lowering the levels of uremic toxins produced by intestinal bacteria-this, combined with the other features of the Mediterranean diet, contributes to a reduction in cardiovascular risk in CKD patients.

Protein Energy Wasting (PEW)

Protein Energy Wasting (PEW) increases the risk of mortality from various causes. Current guidelines recommend that metabolically stable adults with CKD stage 5 on hemodialysis or peritoneal dialysis have a protein intake of 1-1.2 g/kg/day to maintain an adequate nutritional status. To minimize protein catabolism, an energy intake of 25-35 kcal/kg/day is recommended.

Clinical Evidence

A recent investigation conducted in the frame of the CORDIOPREV study evaluated the efficacy of 5 years of consuming a Mediterranean diet rich in extra-virgin olive oil on kidney function. The intervention, compared to a low-fat diet rich in complex carbohydrates, was able to reduce the decline in eGFR in coronary heart disease patients with type 2 diabetes.

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Ajjarapu et al. summarized the results from observational studies investigating associations between dietary patterns and renal outcomes in the general population published over a 10-year period. The authors showed that adherence to the Dietary Approaches to Stop Hypertension (DASH) and Med diets were significantly associated with a reduced risk of CKD incidence.

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