Chronic Kidney Disease (CKD) is said to be a problem for approximately 15% of adults in the United States which amounts to over 30 million people, the data comes from National Health and Nutrition Examination Survey (NHANES) (1). There is a 57% higher chance of cardiovascular mortality in patients with glomerular filtration rate (GFR) below 60 mL/min /1.73 m² and also 7% higher chance of stroke with every 10 mL/min/1.73 m² decrease in GFR (2)The main cause of CKD is diabetes and hypertension, where 30–50% of all CKD is due to the diabetes itself, which equals 285 million people worldwide and that number is expected to rise (2). There is also the higher risk of CKD among patients with (BMI⩾30 kg/m2) up to fourfold (3). Diabetes has a significant impact on the renal health and according to the worldwide cohort approximately 50% of patients diagnosed with type 2 diabetes mellitus (T2DM) had albuminuria and 20% of them had renal insufficiency (4). According to 12-year Chronic Renal Insufficiency Cohort (CRIC) Study the patients diagnosed with moderate and advanced CKD tend to have different estimated glomerular filtration rate (eGFR) slopes between groups. Among those with diabetes the mean eGFR slope was − 2.7 mL/min/1.73m2 /year when non-diabetic group was reported to have − 1.4 mL/min/1.73m2 /year (5). One of the nutritional strategies concerning the CKD is the protein restriction therapy which is either low protein diet (LPD) (0.6–0.8 g/kg/day) or very low protein diet (VLPD) (0.3–0.4 g/kg/day) which is also supplemented with ketoanalogues (KAs) (6). Vegetarianism is now on the rising trend as not only a way of eating but also behaving, It is said to have a positive impact on quality of life and also well-balanced vegetarian diets are nutritionally adequate for all age people (7). There are many studies that highlight some nutrition modifications to postpone the development of CKD, but the question is: Does the change to vegetarianism prevent the progression of CKD?
Vegetarian and vegan diets are becoming increasingly popular around the world. There are many types of vegetarian diets. The most commonly associated with the term vegetarian diet is lacto-ovo vegetarian diet, in which people consume fruits and vegetables as well as dairy products (such as milk and cheese), eggs and honey. Another type of vegetarian diet is pescetarianism which includes also the consumption of fish. Vegan diet on the other hand allows only for consumption of fruits and vegetables (8, 9). Types of vegetarian diets are summarized in Table 1. Because of many differences among those diets it is very difficult to establish their influence on biological parameters. In the US around 5% of adult population consider themselves vegetarian while 3% label themselves as vegans (8). It is also important to consider the influence of religion on diet. For example, in Hinduism vegetarian diet is considered as pure and ideal, it is also reflected in the number of vegetarians in India, where 39% of people consider themselves vegetarians and 81% follow meat consumption restrictions(10).
Table 1
Diet models of vegetarian diet (8, 9).
Diet model | Products excluded from the diet |
Pescetarianism | meat |
Ovo-lacto-vegetarianism | meat, fishes |
Ovo-vegetarianism | meat, fishes, milk |
Lacto-vegetarianism | meat, fishes, eggs |
Veganism | meat, fishes, eggs, milk, honey |
When compared to people who consume meat, vegetarians and vegans have lower levels of many common risk factors such as BMI (-1.72 kg/m2), fasting glucose (-6.38mg/dL), LDL- cholesterol (-22,87mg/dL) and triglycerides levels (-9.35mg/dL) (11). Another meta-analysis shows that based on the changes made to diet total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-cholesterol) levels may be lowered by up to 15% by lacto-ovo vegetarian diet; up to 25% by vegan diet and as high as 35% for vegetarian diet with additional nutrients such as fiber, soy and nuts (12). This is reflected in results of a study, which investigated the effects of vegetarianism and veganism on blood pressure in the population of Adventists in the US and Canada. In said study lacto-ovo vegetarians are shown to experience a decrease of 9.1 mmHg of systolic BP and 5.8mmHg decrease in diastolic BP compared to non-vegetarians (13). Similarly, vegans have a decrease of 6.8mmHg and 6.9mmHg respectively (13). Vegetarians tend to have lower fasting glucose level and higher insulin sensitivity than omnivores with 12% lower β-cell function. The calculated Homeostatic Model Assessment – Insulin Resistance (HOMA-IR) for vegetarians was 1·10 comparing to 1·56 for omnivores (p value 0.001) (14) and according to other study this relationship is corelated with years of being vegetarian (the more years the higher insulin sensitivity) (15). The health effects of vegetarian diet are graphically presented in Fig. 1.
Based on a study conducted in the UK, vegans obtain 2.9% of energy less from protein sources compared to meat-eaters. Their fiber intake was much higher (41% higher for vegan men compared to meat-eating men) as was the consumption of vitamins: B1, C, E and folate. However, they also had the lowest levels of retinol, vitamin B12 and D (16).
Moreover, vegans have the highest intakes of iron and magnesium but lowest intake of calcium and zinc. Their potassium levels were similar (below 5% change between groups) (16). In another study, potassium excretion levels were much higher in vegetarian population compared to non-vegans (62mEq/g of creatinine in vegetarians and 46mE1/g creatinine in control group) (8). The authors of that study found a correlation between potassium excretion levels and blood pressure (BP), discussing the positive effect of potassium on BP (17). Vegetarian diet is beneficial for phosphorus homeostasis in human body, there is positive impact of plant-based source of protein which significantly decreased fibroblast growth factor 23 (FGF23) levels in patient along with the serum phosphorus levels (18). Additionally, it is important to note the decrease in incidence of cancer in people following the diets, with vegetarians showing 8% decrease and vegans with 15% decrease (11).
Chronic Kidney Disease
Chronic Kidney Disease (CKD) is defined as abnormalities of kidney structure with markers such as albuminuria, urine sediment and electrolyte abnormalities. There is also decreased GFR (< 60ml/min/1.73m2) and histological or imaging abnormalities (19). This persistent over 3 month damage is staged as in Table 2.
Table 2
GFR categories (stages) of chronic kidney disease (CKD) according to Kidney Disease: Improving Global Outcomes (KDIGO) (20)
GFR categories (ml/min/1.73m2) |
G1 | ≥ 90 |
G2 | 60–89 |
G3a | 45–59 |
G3b | 30–44 |
G4 | 15–29 |
G5 | 15 |
The diagnosis of stage G3 of CKD is mostly among elderly patients (above 70 years old)This fact shows the limitation of this classification that does not consider the age or ethnicity (21). There are several factors that distinguish CKD from diabetic kidney disease (DKD), one of them is that DKD patients are more anemic than these with non-diabetic CKD. There is an incidence of stage of hyperfiltration in DKD patients at the beginning, but then it starts to decline (22).
There is a significant difference between the prevalence of ESRD between the T2DM and non-diabetic patients. The incidence rate for individuals with T2DM is 1126.12 per 100000 person-years comparing to 245.67 in non-diabetic patients (23).