The Alkaline Diet: What It Gets Right and Wrong

The alkaline diet has been popular for years. It says that some foods make the body "acidic" and cause disease, and that eating mostly "alkaline" foods detoxifies you, slows ageing and prevents cancer.

The science doesn't support the central claim. But look at the list of alkaline foods and you'll notice something: it's mostly vegetables, fruit, nuts and legumes. The diet is right for the wrong reasons.

What the alkaline diet claims

The idea is that foods leave behind acid or alkaline "ash" after digestion. Meat, cheese, grains, sugar, coffee and alcohol are called acid-forming. Most vegetables and fruit, nuts, seeds and legumes are called alkaline-forming. Supporters say a diet of around 70 to 80% alkaline foods keeps the body in balance.

What really happens

Your body controls the pH of your blood very precisely. If it moved much outside its normal range you would be seriously ill, not mildly out of balance. The lungs (by breathing out carbon dioxide) and the kidneys (by adjusting what goes into urine) take care of it continuously.

What food does change is the acidity of your urine. That's your kidneys doing their job, not a sign of your body becoming acidic.

On cancer, the original version of this article said alkaline foods help prevent it. A 2016 systematic review looked at all the published research on dietary acid load, alkaline water and cancer and found no evidence to support that. Tumours can create acidic surroundings themselves, but eating alkaline foods doesn't change that.

What the diet gets right

Strip away the pH theory, and the alkaline diet asks you to:

• eat lots of vegetables and fruit,
• eat nuts, seeds and legumes,
• cut back on processed meat, sugar and alcohol.

That's excellent advice, and very similar to the Mediterranean-style patterns linked with lower rates of heart disease, type 2 diabetes and some cancers. Vegetables and fruit are also rich in potassium, which helps control blood pressure, and fibre.

There is one area where dietary acid load is being studied seriously: kidney disease. For people with chronic kidney disease, more fruit and vegetables may help the kidneys. That's a medical question to discuss with a specialist, not a reason to test your urine at home.

A vegetable-first shopping list

These are the foods the alkaline diet recommends, and the ones worth filling your basket with anyway.

Vegetables: beets, broccoli, Brussels sprouts, cabbage, carrots, cauliflower, celery, collard greens, cucumbers, dandelion greens, garlic, green beans, kale, lettuce, mushrooms, onions, parsley, peppers, radishes, sea vegetables, spinach, squash, sweet potatoes, watercress.

Fruit: apples, apricots, avocados, bananas, berries, cherries, citrus fruit, dates, figs, grapes, mangoes, melons, papaya, pears, pineapple, tomatoes.

Nuts and seeds: almonds, flaxseed, pumpkin seeds, sunflower seeds.

Legumes and grains: lentils, beans, millet, buckwheat, quinoa.

Flavour: fresh herbs, cinnamon, ginger, curry spices, lemon and lime.

What about the "acidic" foods?

You don't need to cut out whole grains, beans, fish, eggs or dairy. The alkaline diet labels some of these acid-forming, but they're part of most healthy eating patterns. Whole grains and legumes are linked with better health, not worse.

The foods genuinely worth limiting (processed meat, sugary drinks, refined snacks and alcohol) are the same ones every eating guide recommends limiting.

The bottom line

Your body manages its own pH beautifully, and no diet will change your blood's acidity or prevent cancer by "alkalising" you. But the alkaline diet's shopping list is a fine one. Eat the vegetables, fruit, nuts and legumes. Skip the pH strips and alkaline water.