The kidneys are greatly affected by diet. When foods are broken down, absorbed and metabolised they either produce acid or alkali. The kidneys work harder when there is too much acid in the diet – acid forming foods including red and white meat, fish, cheese, eggs, sugar, alcohol and some grain products. Most fruit and vegetables are alkali-producers and therefore beneficial for kidney health. If the diet contains too many acid-producing foods for a long time, or if the kidneys are damaged and don’t function well, it can lead to a condition called metabolic acidosis (constant acid overload of the body that can lead to poorer health and disease).
Here is a selection of studies that have investigated different diets on kidney health:
- 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 chronic kidney disease (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 kidney damage, animal protein increases the risk of further kidney deterioration (Knight et al., 2003). 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 risk 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 product 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 suggests 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.