How the acid‑alkaline effects of what you eat may influence long‑term health — and why simply avoiding “acidic” foods on the plate isn’t the whole story

I tried a quick home test with pH paper to see whether my diet produced acidic urine. It’s a crude indication of dietary acid load (DAL): if your diet yields more acid than your body comfortably handles, the kidneys work harder to excrete it and the urine tends to be more acidic. That doesn’t mean the occasional red results in a death sentence, but researchers are paying renewed attention to DAL because sustained excess acid exposure may contribute to a range of chronic conditions — from kidney problems to metabolic and cardiovascular disease.

This idea isn’t the same as the long‑debunked “alkaline diet” which claims that alkaline foods cure cancer. Instead, scientists are studying how the balance of acid‑forming and alkali‑forming metabolites produced by different foods affects physiology over the long term. The concept has a practical payoff: adjusting food choices to reduce overall DAL is a feasible strategy that tends to overlap with other healthy‑eating recommendations.

Why plate pH can be misleading

What matters is not the acidity of a food on your plate but the properties of its metabolites after digestion. Citrus fruits, for example, taste acidic but are metabolised to alkaline compounds and tend to lower DAL. By contrast, many animal proteins and some processed foods produce acid metabolites. Salt (chloride) and additives such as phosphoric acid (used in some soft drinks and processed products) are additional contributors to DAL.

From the 1960s onward researchers noted differences in urinary pH between vegetarians and omnivores, and older ideas about “acid ash” evolved into modern measures such as potential renal acid load (PRAL). PRAL estimates how acidic or alkaline 100 g of a food becomes after metabolism, based on its protein, phosphorus, calcium, magnesium and potassium content. Foods with negative PRAL values are alkali‑forming; positive values are acid‑forming. Typical patterns: leafy greens are strongly alkali‑forming, many meats and cheeses are acid‑forming, and most fruits and vegetables fall on the alkaline side.

How much acid is too much?

Healthy kidneys can handle a substantial acid load, but chronic excess creates a steady demand on renal function and may promote “low‑grade metabolic acidosis” — a subtle, persistent shift toward the lower end of normal blood pH that some researchers link with poorer outcomes. Observational and early trial evidence associates higher DAL with increased risk of chronic kidney disease and suggests links to obesity, hypertension, diabetes, liver disease and even mood disorders, though many of these links still need confirmation in larger randomized studies.

PRAL‑based assessments let researchers and individuals estimate daily DAL. While estimates vary, a daily PRAL substantially above about 60 mEq/day is generally considered high and could signal the need for dietary adjustment. Many people eating typical Western diets — relatively high in animal products, salt, refined grains and ultra‑processed foods and low in leafy vegetables — tend to have elevated DAL.

Practical implications and caveats

A low‑DAL eating pattern often resembles other healthy diets: more plant foods (especially leafy greens), fewer processed items, less red and processed meat and lower added salt. That said, not all plant foods are equal for DAL (some fruits and vegetables contain compounds that raise acid load), and processed plant‑based products can include acidic additives. Measuring PRAL precisely requires food‑level data and calculations, but general guidance is straightforward: favour whole, minimally processed plant foods, reduce intake of highly acid‑forming animal products and avoid excessive use of salt and phosphoric‑acid‑containing drinks.

There is promising early evidence that reducing DAL can have metabolic benefits beyond simply cutting calories. Small dietary trials have shown greater fat loss on more alkaline plant‑based plans than on some other approaches, and ongoing research includes randomized trials in people with diabetes to test DAL‑targeted diets more rigorously.

Bottom line

DAL does not resurrect unscientific alkaline dogma, but it offers a useful, evidence‑driven perspective on how food composition influences physiology. Shifting toward a diet that lowers overall acid load — more leafy greens and other alkalinising plant foods, fewer processed and acid‑forming animal products, and less salt and phosphoric additives — is a practical step that aligns with established healthy‑eating advice and may also reduce long‑term strain on the kidneys and other systems.

Adapted from: Graham Lawton, “A radical rethink of what makes your diet healthy or bad for you” (original article by Graham Lawton, 13 October 2025; updated 21 November 2025).

Graham holds a first-class honours degree in biochemistry and an MSc in science communication, both from Imperial College London