Plant proteins have often been touted as a healthy alternative to animal protein. Early studies suggested that soya proteins lowered serum cholesterol, and subsequent research found that a number of legumes share this property. Higher intake of vegetable protein and oil was also associated with reduced heart disease risk in the Nurses’ Health Study. Increasing vegetable and reducing animal protein intake has been linked to less encephalopathy in liver disease. Later trials have suggested that increased vegetable as opposed to animal protein results in less hip fracture in women, perhaps related to the lower acid load, which may reduce urinary calcium losses.

Most recently it appears that plant foods also reduce microalbuminuria, strong evidence of a beneficial effect on renal function. The data came from the Multi-Ethnic Study of Atherosclerosis (MESA) (Am J Clin Nutr 2008;87: 1825-36), in which 5,042 participants without baseline evidence of cardiovascular disease (CVD), diabetes or microalbuminuria were assessed.

After adjustment for confounders, a plant food diet together with low-fat dairy was associated with a 20% lower albumin to creatinine ratio (ACR) across the quintiles (P = 0.004). Over half of the effect appeared to be due to dairy. On the other hand, the non-dairy animal foods were associated with an 11% higher albumin to creatinine ratio across quintiles (P = 0.03).

Plant foods are emerging as mildly beneficial for renal function while animal foods — with the notable exception of dairy — are associated with impaired renal function.

The calcium connection

The difference between dairy and non-dairy animal foods could well be calcium. It can neutralize the acid products of protein metabolism, possibly conferring benefit on kidney function in the long term and thus reducing microalbuminuria. Calcium may also underlie an apparent protective effect of dairy food in osteoporosis and hip fracture. This must, of course, be balanced against calcium’s negative effect on CVD in postmenopausal women.

The effects of the individual components of a plant-based diet — nuts, seeds, legumes and vegetables — need to be teased apart. None of these, on their own, showed significant negative associations with microalbuminuria in the MESA trial — only dairy, and to a lesser extent whole grains, did.

But on balance, we’re left with further support for the conventional wisdom that informed the DASH diet (Dietary Approaches to Stop Hypertension), namely, the benefits of a lactovegetarian diet. While DASH targets blood pressure, it’s also likely to help prevent chronic kidney disease.