Alkaline Diet: A Scientific Review

Can you change your body’s composition, radically improve your health, and lose weight just by tweaking your internal acidity with food? That’s what the alkaline diet proposes.

Also known as the acid-alkaline diet, alkaline ash diet, or acid/alkaline ash diet, this eating approach first hit the scene in 2002 with the publication of the best-selling book The pH Miracle: Balance Your Diet, Reclaim Your Health. In it, co-author Robert O. Young, a self-described naturopathic practitioner and scientific researcher, claimed he had discovered a “new biology” that would enable people to lose weight and prevent disease—by using diet to control the acid level of blood. 

In recent years, Young has been discredited as a health expert. Following a three-year criminal probe, he was convicted in 2016 on two charges of practicing medicine without a license and pleaded guilty to two additional felony counts, ultimately serving a prison sentence in 2017. As part of the plea agreement, Young admitted in court that he had zero scientific or medical training.

Nevertheless, the diet he pioneered has its believers. Proponents of the alkaline diet avoid foods thought to produce acid in the body, such as meat and sugary snacks. Instead, the diet emphasizes “alkaline-promoting” foods, such as fresh fruits and veggies. The thinking is that this keeps the pH level of blood in a healthy zone that prevents wear and tear on the body and reduces one’s risk of developing diseases such as osteoporosis and cancer. Easy weight management is another common promise.

So far, the alkaline hypothesis hasn’t held up to scientific scrutiny. “There really isn’t evidence to support it,” says registered dietitian Sandie Hunter, manager of clinical nutrition at Northwestern Medicine Delnor Hospital in Geneva, Illinois. “[The alkaline diet] may promote weight loss because it’s restrictive, not because of the alkaline theory.” Ditto for reducing the risk of osteoporosis and cancer, Hunter says—some aspects of the diet may be beneficial for disease prevention, but it’s unlikely that acid levels in blood are the reason. 

Still curious? Here’s what you need to know about the alkaline diet, including the theories behind the regimen, the alkaline-promoting foods the diet allows, the acidifying foods the diet discourages, and a closer look at those “breakthrough” claims.

What is the alkaline diet?

The alkaline diet is based on the theory that low body pH (acidity) can be harmful to one’s health, while high pH (alkalinity) is protective. In chemistry, pH is expressed using a 14-point scale, with zero being totally acidic and 14 being totally alkaline. 

Proponents contend that the foods you eat can alter the pH level of blood—and therefore influence every system in the body. The theory is that when the body breaks down food to create energy, it leaves behind a residue known as ash. Ash can be acidic or alkaline, depending on what you’ve eaten. 

According to alkaline theory, eating an acid-forming diet puts the body into a state of inflammation known as low-grade chronic metabolic acidosis. In addition, the theory continues, systemic stress arises from the body’s constant effort to neutralize pH levels. As a result, appetite-controlling hormones are disrupted, and cells receive a diminished supply of oxygen and nutrients, leaving the body susceptible to disease and weight gain. 

On the flip side, according to believers, “alkalizing” foods do not form acidic ash. This supposedly eases strain on your system and keeps inflammation at bay. The diet’s fans say this can result in more energy, easier weight loss, and reduced risk of disease.

Foods to eat on the alkaline diet

People on an alkaline diet are encouraged to consume 60–80% of calories from alkalizing foods and limit acid-forming foods to 40% of calories. This breakdown usually includes 50 to 63 grams of protein per day. Some people following the alkaline diet prefer a ballpark shortcut: For every 10 foods, six should be vegetables, two fruits, one protein, and one starchy alkaline-forming food (like sweet potato).

According to alkaline theory, a food’s inherent acidity doesn’t necessarily correspond with its acid load in the body. Citrus fruits like oranges, for example, are encouraged on the plan even though oranges themselves are acidic. In general, those on the diet are guided toward the following foods:

• Most fruits
• Most veggies
• Some nuts and seeds
• Some legumes
• Unsweetened herbal tea

Many proponents of the alkaline diet claim that tap water is acidifying and therefore should be avoided. Instead, they are generally advised to drink bottled spring water, which contains trace minerals thought to be alkaline-forming, or commercially bottled alkaline water, which is treated with an ionizing process or fortified with alkaline minerals like potassium and calcium to raise its pH.

The following chart offers a closer look at how people tend to eat when following an alkaline diet. Most versions of the plan emphasize choosing foods and beverages from the left half of the chart and limiting selections on the right half of the chart.

Foods to avoid on the alkaline diet

As noted in the chart above, proponents of the alkaline diet say the following foods and beverages promote harmful acid formation in the body and should be limited:

• Meat
• Poultry
• Fish
• Dairy
• Eggs
• Most grains
• Processed foods
• Refined sugar, including sugar in drinks
• Alcohol
• Caffeine

What science says about the alkaline diet

There is no good evidence that the alkaline diet lives up to its health claims concerning cancer, osteoporosis, or weight loss, say independent experts—at least not for the reasons it claims. 

Dr. James Simon, M.D., a nephrologist at Cleveland Clinic, says that it’s true that certain foods produce acids when broken down during digestion. It’s also true that human blood is slightly alkaline—usually around 7.4 on the 14-point scale. But here’s the big sticking point: The pH level of blood remains alkaline regardless of what the average person eats. “[The body] has very aggressive, very redundant, and very robust ways of handling acid,” Dr. Simon explains.

Those processes involve the kidneys, which eliminate some acid through urine and some by producing an ion called bicarbonate. Bicarbonate binds with free hydrogen ions for use by the lungs in producing carbon dioxide, which you then exhale. The liver also plays a role in acid management. 

In rare cases, the body’s acid levels can rise too high, a state indeed known as metabolic acidosis. Metabolic acidosis can occur as a complication of diabetes, kidney disease, and other serious illnesses. In other words, if you’re a healthy person with normal kidney and lung function, diet has no meaningful impact on your body’s pH levels, Dr. Simon says. Consuming “acidifying” foods won’t reduce the bloodstream’s pH level, and an alkaline diet won’t raise pH.

As for ash—that so-called byproduct of digestion—it simply doesn’t exist, Dr. Simon says. Once the body breaks down foods and sends excess acid packing, “there’s no residue,” he explains. “[It’s not like] silt building up inside of our chimneys.”

Followers of the alkaline diet often attempt to measure the body’s pH level through litmus-based urine testing. But the acidity of urine doesn’t reflect acidity levels in the bloodstream or elsewhere in the body, says internal medicine specialist Dr. William Yancy, M.D., director of the Duke Diet and Fitness Center in Durham, North Carolina. Urinary pH can vary widely after the consumption of different foods—anywhere from 4.6 to 8.0, Dr. Yancy says, noting, “You might have more acid in your urine when your kidneys are actively getting rid of it.”

Also worth noting: Certain body processes depend on high acidity. The digestive system, for instance, needs to be highly acidic (with a pH level of 1.35 to 3.5) to break down the foods you eat, Hunter notes.

Potential health benefits of the alkaline diet

Considering that just 10% percent of U.S. adults eat the recommended amount of fruits and veggies every day, one upside of the alkaline diet is that it emphasizes fresh produce, Hunter says.

Amping up intake of plant-based foods could provide important cell-protecting phytonutrients, as well as at least one essential mineral many adults are lacking: potassium, which helps regulate blood pressure and support healthy cell functioning.

For people whose regular diets tend to favor animal-derived foods, sugary snacks, and other prepackaged fare, switching to an alkaline diet could lead to weight loss by creating a caloric deficit, Hunter says.

Potential health risks and downsides of the alkaline diet

The alkaline diet raises a number of concerns among the experts who spoke with WeightWatchers®. Here are some of the diet’s potential drawbacks. 

• It may lead to nutritional shortfalls. The body needs a varied diet to get the full range of nutrients required for optimal health. Since the alkaline diet limits major food groups—including grains, dairy, and all animal protein—maintaining balanced nutrition could be challenging, Hunter says.
• Meals might not satisfy. With a big list of foods to avoid, you might not find the alkaline diet enjoyable or satisfying unless you’re used to (or excited about) eating vegan-style. “I tend not to recommend really restrictive diets that may be difficult to follow in the long term,” Hunter says.
• It overlooks exercise. Both Hunter and Dr. Yancy point out that physical activity is an important part of a viable health and weight-loss plan. The alkaline diet does not include guidance on fitness or exercise.
• It may create a false sense of security. No published studies of good quality support claims about the alkaline’s diet’s ability to ward off serious disease, Dr. Yancy says. Placing too much faith in the diet’s powers of prevention could cause people to overlook early warning signs of illness.
• It may not be safe for people with kidney conditions. Anyone with uric acid kidney stones or chronic kidney disease should think twice (and check with their doctor) before trying an alkaline diet, Dr. Simon says. That’s because many alkaline foods are high in potassium—a nutrient processed by the kidneys. When kidneys are compromised, high potassium intake could lead to complications, Dr. Simon says.

The alkaline diet and cancer

Right now there’s no evidence to support the theory that an alkaline diet can prevent cancer. A 2016 research review in BMJ found that most studies aimed at exploring a correlation were of poor scientific quality and could neither prove nor disprove the diet’s supposed preventive powers. Most research on alkalinity and cancer—such as this analysis examining the interaction of bladder cancer cells and cancer drugs in different pH settings—have been conducted in test tubes, not humans. Such results don’t necessarily translate to the complexities of the human body, according to the American Institute for Cancer Research. (Also, the results of that particular study were mixed: Three of the six drugs studied actually killed more cancer cells in acidic environments, and one was unaffected by pH.)

The alkaline diet and osteoporosis

Among the alkaline diet’s biggest claims is that the eating approach can prevent osteoporosis, a medical condition marked by brittle or fragile bones resulting from loss of tissue.

First, some background: Bone health can take a hit if a serious illness such as kidney disease causes elevated acid levels in the bloodstream—that state known as metabolic acidosis, Dr. Simon says. In such cases, bones may release bicarbonate in the form of calcium carbonate to help buffer acid in the blood.

Remember, though: Everyday diet doesn’t send healthy people into metabolic acidosis to begin with. “That’s not a normal state [that arises from] eating extra acid every day,” Dr. Simon says. 

Indeed, a 2011 systematic review and meta-analysis of 55 studies, published in Nutrition Journal, found “no evidence that an alkaline diet is protective of bone health.” 

And although the alkaline diet does deliver a measure of the bone-building minerals calcium and phosphorus via fruits and veggies, it restricts meat and dairy, which for many people would be significant sources of those bone-loving nutrients. “Some of the very foods the diet restricts could work against bone health,” Hunter says.  

In addition, weight-bearing forms of physical activity such as walking and elliptical training are essential for strong bones—and the alkaline diet lacks guidance on exercise, Dr. Yancy adds. 

The alkaline diet and weight loss

While some have reported losing weight on an alkaline eating plan, the independent experts who spoke with WW say such results are unlikely due to pH changes in blood. “I have no idea how that [would] help with weight loss,” says Dr. Yancy, who notes that he hasn’t seen any clinical trials suggesting it does. The more likely explanation for losing pounds on this plan: slashing calories from sweets, alcohol, and processed foods and switching to lower-calorie fruits and veggies.

Still, some alkaline adherents contend that eating too much acid-forming food raises levels of the stress hormone cortisol as the body scrambles to neutralize pH levels. According to the theory, this messes with hunger hormones and insulin levels, promoting weight gain. But the Cleveland Clinic’s Dr. Simon disputes the premise, noting that the body does not “stress out” in response to acid-forming foods. 

Some other practitioners of the alkaline diet bill weight loss as more of a potential side effect than a selling point.

As with bone health, a shortcoming of the alkaline diet for weight loss is that the plan doesn’t incorporate physical activity, which research shows is a key component of long-term weight management. 

The upshot: Does the alkaline diet work?

There’s no credible evidence that an alkaline diet can improve health or speed weight loss by altering the pH level of blood or other parts of the body. In cases where the diet results in weight loss, the effect is likely due to calorie restriction—not the acid load of food. Though the alkaline diet emphasizes healthy fruits and vegetables, it strictly limits many other food types, which could make the diet (and any weight loss it brings about) difficult to maintain. The alkaline diet does not address physical activity, an important aspect of supporting health.

An effective wellness and weight-loss program is one that is sustainable, supports healthy eating patterns, and takes total wellbeing into account. 

--

Colleen de Bellefonds has been covering health and wellness for over a decade for publications including U.S. News & World Report, Women's Health, Vice, Prevention, Healthline, and more. She lives in Paris, where she shares her croissants with her dog and plans her weekends around runs by the Seine.

--

This article was reviewed for accuracy in July 2021 by Angela Goscilo, MS, RD, CDN, manager of nutrition. The WW Science Team is a dedicated group of experts who ensure all our solutions are rooted in the best possible research.

Related articles

• Whole30: What Is it, and Does it Work?
• Here's the Deal on the Ketogenic Diet
• Is Intermittent Fasting Safe?