So you spent the weekend gorging on burgers and funnel cake (it’s summer, after all) only to find yourself reaching for the antacid on Sunday night—we’ve all been there. While it’s no surprise that certain large, fatty meals can contribute to digestive upsets such as heartburn, specific foods might be to blame as well. Some experts believe acid-forming foods (including some fish, meat, and grains) can lead to tummy troubles, weak bones, and lower-back pain, while foods with lower acidity—hello, fruits and vegetables—may keep the body in better balance.
What’s the Deal?
The idea behind the low-acid regimen often referred to as an "alkaline diet" is that eating more fruits and vegetables can balance the body’s pH, mitigating issues including heartburn and acid reflux (among others). Now, let’s teleport back to high school chemistry class for a second: pH is the measure of how acidic or basic a solution is. A pH of 1.0 is highly acidic, while a pH of 14.0 is very basic, and 7.0 is neutral. Our blood usually maintains a pH of between 7.38 and 7.42, while the pH of stomach acid can be as low as 1.35 . When these numbers get out of whack, it can spell trouble for our bodies.
But just because a food is acidic or has a low pH does not necessarily mean it’s considered “acid-forming”—that’s a matter of how the food changes the acidity of body fluids in the kidney and urine post-ingestion. This is measured using potential renal acid load (PRAL) scores. One study that tested various foods for their PRAL score found that fruits and vegetables had low PRAL scores, while processed foods, dairy, and meats had high scores . A higher PRAL score (indicated by a positive number) means that a particular food is very acid-forming, while a lower PRAL score (indicated by a negative number) classifies it as alkaline, meaning that it produces more basic compounds rather than acidic ones.
So what foods are allowed? It's complicated. Most vegetables are a-okay, as are most fruits and soy products, and some nuts (including cashews and almonds), grains (including quinoa and whole-grain rice), oils (including , and legumes (including lentils and green beans). Meat, fish, poultry, dairy, processed foods (including white sugar and white flour), and caffiene are no-nos. The tricky part is that there are many foods that fall somewhere in the middle: Dairy products can range in PRAL score from around one, all the way up to over 30. Even vegetables—which are largely considered a healthy part of the alkaline diet—range from -14 (good!) to 0 (not as good!). (Fruits are in the same boat.)
A key point to remember is that just because a certain product is in itself very acidic doesn’t mean it is acid-forming. Lemons are a great example. These sour citrus fruits are themselves pretty acidic with a pH of 2.0. However, a lemon’s PRAL score (per the study mentioned above) is -2.5, meaning it is alkaline when digested within the body.
Why Do People Care?
With health issues such as food intolerances and allergies, celiac disease, and other chronic health conditions on the rise, it seems like people will do just about anything to alleviate symptoms. Since the alkaline diet offers hope of eliminating or lessening unpleasant symptoms like acid reflux and heartburn, it’s become a popular option among the health-conscious community—and among well-known celebrities including Jennifer Anniston and Victoria Beckham.
The alkaline diet's supposed benefits likely stem from an increased intake of fresh produce, not necessarily a change in the body's pH. There are few downsides (and lots of benefits) to consuming a healthy dose of veggies. There is also some skepticism regarding our ability to actively change pH through diet: Some experts argue that while eating less acid-forming foods may change the pH of our urine, it can't really change the pH of blood, which our bodies meticulously maintain on their own. And with a strictly "alkaline" diet, you’ll be missing out on (for example) healthy doses of omega 3s in fish and other healthy fats it suggests scaling back on.
And some of the benefits attributed to a low-alkaline diet might in reality come from just upping produce intake. One three-year study found that men and women who consumed a low-acid diet with potassium-rich fruits and vegetables lost less muscle mass than those with a lower potassium intake . This may have to do with the fact that potassium is traditionally considered an important mineral for proper muscle function, so getting enough of it can keep your tissues in tiptop shape.
Diets high in fresh produce have been linked to lower risk of heart attack and stroke  . What’s more, they can boost your mood. Plus, if you cook meals paired with veggies, one study suggests it makes others think you’re a better cook .
Scientists also speculate that when the body’s acidity is too high, it pulls minerals such as potassium, magnesium, and calcium from bones in order to help neutralize itself. Pulling too much calcium from bones can lead to weaker skeletons . This may also explain why some countries that chow down on calcium-rich dairy can still have high levels of osteoporosis . Just keep in mind this link is not definitive—other research suggests certain dairy products such as milk and yogurt can indeed improve bone density . And when combined with adequate calcium intake, diets higher in protein (another acid-forming food group) might actually result in fewer fractures and greater bone mass .