Clinical implications of a healthy diet in individuals with renal dysfunction

Laburpena

Background: Chronic Kidney Disease (CKD) affects an important and increasing percentage of the population nowadays because it's associated to other pathologies such as high blood pressure, diabetes or heart disease. Besides, renal function naturally decreased with ageing. CKD is a pathology that involves multiple changes, from catabolic and nutritional processes to bone and heart disease complications that determine the rate of CKD progression and its prognosis. Nutrition plays an important role in the development of multiple pathologies, including diabetes, high blood pressure and most likely as well CKD. Risk of malnutrition depends on multiple factors among the elderly population or CKD patients: in some cases malnutrition is related to a deficient intake of nutrients attributed to a decrease in appetite; other ailments are responsible such as metabolic diseases that induce body protein-catabolism driving the patient to a wasting state of protein reserves. This would be the case of sustained inflammation or metabolic acidosis. It is assumed that restrictive diets contribute to the risk of malnutrition in this population because of the difficulties to adhere to them. There is not evidence to suggest age-related decrease in glomerular filtration rate is one of the potential risk factors in the malnutrition risk of the elderly. On the other hand, undiagnosed CKD in this population group could let the door open to multiple risk factors because many molecular substances are not metabolized by the kidney. This Doctoral Thesis contains three peer-reviewed Scientific publications evaluating the nutritional level base diet among different population groups with kidney dysfunction. We analyzed their clinical implications as follows: Study 1: Objetives: Diet Quality evaluation and degree of adherence to renal-specific guideline recommendations in a single-center hemodialysis population. Methods: Cross sectional analysis including 91 patients undergoing maintenance hemodialysis at a hospital in north Tenerife (Spain). Clinical data and three-day dietary records were collected. We compared patient’s reported nutrients intake with guideline recommendations. We also evaluated their alignment with current American Heart Association (AHA) dietary guidelines for cardiovascular prevention. Results: 77% and 50% of patients consumed less amounts of energy and proteins recommended. Saturated fat intake was superior to the suggested one in 92% of the cases studied. Just 22% of them ate enough fiber, but just a small percentage reached the vitamin required (except for cobalamin). In the same way, we observed an inadequate intake of many minerals, some in excess like phosphorus, calcium, sodium and potassium and others in deficiency, like magnesium. Most of the patients consumed enough iron and zinc through their diets. Conclusions: A large proportion of patients undergoing hemodialysis at this Spanish Center did not adhere to the recommendations from renal nutritional guidelines. Their diet quality was poor, and pro-atherogenic as evaluated from the American Heart Association dietary guidelines for cardiovascular prevention. Study 2: Objectives: Evaluate the possible relationship between kidney dysfunction and energy intake in elderly community-dwelling individuals. Methods: Cross sectional study including 1087 men aged 70 year from the Uppsala Longitudinal Study of Adult Men (ULSAM). Dietary intake was assessed using 7 days food records and glomerular filtration rate (eGFR) was estimated through serum cystatin C concentrations. Energy intake was normalized by ideal body weight and macronutrients intake was energy-adjusted. Results: The median normalised daily energy intake was 25 Kcal (105 KJ) and directly correlated with eGFR in the univariate analysis. Across the decreasing quartiles of eGFR, a significant linear trend towards decreasing normalised energy intake was observed (p= 0.01). We carried out multivariable regression models where we included lifestyle and several co-morbidities as confounding variables. We found that regular physical activity (standarized = 0.141; p= 0.01), tobacco consumption (standarized = - 0.083; p= 0.01), hypertension (standarized = - 0.104; p= 0.01), hyperlipidaemia (standarized = - 0.063; p= 0.04) and eGFR (per standard deviation increase, standarized = 0.064; p= 0.04) were independent predictors of energy intake. Conclusions: There was a direct and independent correlation between renal function and energy intake in a community-dwelling population of Swedish men. We speculate on a possible connection between underlying kidney dysfunction and malnutrition in the elderly. Study 3: Objectives: Evaluate if dietary acid load is associated with blood pressure and incidence of hypertension among the elderly men population, evaluating the possible modifying impact of kidney dysfunction. Methods: Cross-sectional and longitudinal analysis including 673 males age 70 years from the Uppsala Longitudinal Study of Adult Men (ULSAM). Of those, 378 subjects were re-examined after 7 years. Dietary intake was assessed using 7 days food records. Dietary Acid load was estimated at baseline by potential renal acid load (PRAL) and net endogenous acid production (NEAP). Ambulatory blood pressure monitoring was performed in both time points. Kidney function was estimated by cystatin C plasmatic levels. Results: Median estimated PRAL y NEAP were 3.3 y 40.7 mEq/d respectively. On the cross sectional part of the study, PRAL was not associated with ambulatory blood pressure measurements (p > 0.05). During follow up, PRAL did not predict ambulatory blood pressure monitoring changes (p > 0.05). When we excluded individuals with high blood pressure or non-dippers, PRAL was not a predictor for new incident cases (p > 0.30). Renal function did not change these relationships. Similar results were found with the use of NEAP as the exposure. Results: We did not find any association between estimated dietary acid load and high blood pressure, neither cross-sectionally nor longitudinally in a communitydwelling Swedish elderly population. Underlying kidney dysfunction did not modify this relationship.