The kidneys are affected by diet to a high degree. During digestion, when foods are broken down, absorbed and metabolised they either produce acid or alkali. The main acid forming foods are red and white meat, fish, cheese, eggs, sugar, some grain products and alcohol and the kidneys are worked harder when there is too much acid in the diet. If the diet consistently contains too many acid-producing foods or if the kidneys are damaged and don’t function well, it can lead to a condition called metabolic acidosis (which is a constant acid overload of the body that can affect numerous biochemical processes and lead to poorer health and disease).
Most fruit and vegetables are alkali-producers and therefore beneficial for kidney health. Among people with chronic kidney disease (CKD), who have compromised kidney function and need to reduce the amount of acid their diet produces, increasing fruit and vegetable intake has proven to be a highly effective approach (Goraya et al., 2013). A scientific team of experts on kidney health studied dietary acid load and how it affects the kidneys. They found that people with the most acid-producing diets had the highest risk of CKD (Banerjee et al., 2014) and that in people who already have CKD, a diet high in acid-producing foods increases the risk of end stage renal disease (Banerjee et al., 2015).
Research has shown that among people with any degree of kidney damage, consumption of animal protein increases the risk of further kidney deterioration (Knight et al., 2003). And Moe et al. (2011) agree that for patients with CKD, the origin of protein in their diet maters – non-animal protein is more protective whilst animal protein increases markers of kidney damage. This is due to higher phosphorus content of animal protein and higher proportion of sulphur amino acids contributing to more acid.
The lifetime prevalence of kidney stones is around 10 per cent in developed countries (Tourney et al., 2014). The Oxford arm of the comprehensive EPIC study examined the relationship between diet and kidney stones in over 51,000 people in the UK (Tourney et al., 2014). Analyses confirmed that meat and meat products consumption increases the risk - those in the top third of intake had a 64 per cent higher risk compared to those in the bottom third. Data from this study also suggest that diets high in fruit, fibre and magnesium can offer protection against kidney stones. Higher magnesium intakes (plant-based foods are the main sources) can reduce the risk of kidney stones by binding oxalate (the main crystal and stone forming compound). On the other hand, a diet high in animal protein may result in an increased stone risk by producing an acid load that increases urinary calcium and oxalate levels and also produces uric acid (another compound that can form kidney stones).
An earlier study by Borghi et al. (2002) supports these findings. Their conclusion was that for people with recurrent calcium oxalate kidney stones, reducing animal protein and salt intake is crucial for successful treatment.
Heilberg and Goldfarb (2013) reviewed data on diet and kidney stones and reached the conclusion that to prevent and treat kidney stones, a plant-based diet is very important. According to their research this applies to oxalate, purine and cystine stones – for all these animal protein is the main risk factor. They recommended increased intake of fruit and vegetables and wholegrains and an overall vegetarian diet.
A vegan diet with limited acid-producing foods and high in fruits and vegetables can protect the kidneys in many ways and if the kidney function has been compromised, it can help the kidneys recover or minimise further damage. Ströhle et al. (2011) showed that a vegan diet has a virtually neutral acid-alkali balance and can be therefore very health protective.
For references and more information, see The Incredible Vegan Health report.