We will never argue with the fact that fruit is glorious; fresh, juicy, sweet and energising. However, we also know that fruit is acidic in nature – and we’ve been led to believe that too much of it can be problem for our bones, which technically like to stay in neutral. However, the acidity of fruits is a well-known characteristic that contributes to their taste and nutritional value. And not all tales are true.
Concerns about how acidic fruits might affect bone health require a nuanced understanding of the biochemistry of acids, the role of diet in bone metabolism, and the body’s regulatory systems. That might sound a bit of a mouthful, pardon the pun, but getting to grips with the balance and science of your body is key.
A biochemical overview
Looking at the composition in fruits, it’s understandable that fruits vary in acidity based on their content of organic acids such as citric acid, malic acid and ascorbic acid – otherwise known as Vitamin C. Common acidic fruits include:
- Highly acidic fruits: Lemons, limes, grapefruits, and oranges.
- Moderately acidic fruits: Apples, strawberries, pineapples, and cherries.
- Less acidic fruits: Bananas, melons, and papayas.
Your pH balance and bone health
While fruits are acidic outside the body, their acidic impact on internal pH and bone health depends on how they are metabolised. The human body keeps tight regulation on its internal pH, maintaining a slightly alkaline blood pH of around 7.4. This regulation is crucial for cellular function and is achieved through mechanisms such as:
- Buffer systems: Bicarbonate in the blood neutralises excess acids or bases.
- Respiratory regulation: Breathing controls carbon dioxide levels, which affect blood acidity.
- Renal function: The kidneys excrete hydrogen ions and reabsorb bicarbonate to maintain pH balance.
The big question: does fruit acidity harm bones?
The Acid-Ash Hypothesis
This suggests that diets high in acid-forming foods, such as meat, dairy, and fish, eggs, and processed grains, can increase acid load in the body, leading to calcium leaching from bones to neutralise this acidity. This could weaken bones over time.
However, the real surprise is that fruits, despite their acidic taste, are generally classified as alkaline-forming foods because their metabolites – particularly potassium bicarbonate – promote alkalinity after digestion.
- Citric acid in citrus fruits metabolises to bicarbonates, leaving an alkaline residue.
- Fruits high in potassium, like bananas and oranges, support acid-neutralising mechanisms.
Scientific Evidence
The good news is that current research does not support the idea Acid-Ash Hypothesis that dietary acid load will significantly affect bone health. A review of clinical studies found no direct link between acid-forming diets and osteoporosis. In addition, the kidneys and lungs efficiently manage acid-base balance, reducing reliance on bone minerals. And happily, fruits and vegetables, even acidic ones, are associated with better bone health due to their content of vitamins, minerals, and antioxidants.
Other factors like calcium and vitamin D intake, physical activity, and genetic factors play a more significant role in bone health.
The real nutritional contribution of fruit with regard to bone health
The fact of the matter is that fruit provides essential nutrients that support bone health, countering any potential negative effects of acidity.
Vitamin C: This is crucial for collagen synthesis, which forms the framework of bones, and is found abundantly in citrus fruits, strawberries, and kiwis.
Potassium: This key mineral helps to neutralise dietary acids, protecting bone mineral density. Bananas, oranges, and melons are excellent sources.
Magnesium: Valuable in aiding calcium absorption and bone formation. Present in fruits like bananas, avocados, and figs.
Polyphenols and Antioxidants: These protect bone cells from oxidative stress and inflammation. Found in berries, cherries, and pomegranates.
Fructose and Natural Sugars: While important in providing energy for cellular processes involved in bone remodelling, moderation is key to avoid excessive sugar intake, which may indirectly harm bone health through metabolic pathways.
Make sure your diet includes a variety of fruits, but also make sure you combine them with vegetables, nuts, seeds and protein and dairy sources for a balanced diet. And most important – focus on those things really responsible for acidity in your diet, such as soft drinks and processed snacks, which contribute to dietary acid load more significantly than fruits. Drink plenty of water, and choose whole fruits rather than dried fruits or fruit juice, as these can affect bone health in the long-term.
So it’s good to know that the body’s sophisticated pH regulation ensures that the small amount of acidity from dietary sources does not harm bones. By emphasizing variety, moderation and balance, fruit can definitely be an integral part of a bone-friendly diet.
NOFSA (National Osteoporosis Foundation South Africa)
NOFSA is the only non-profit, voluntary health organisation dedicated to promoting lifelong bone health. We focus on reducing the widespread prevalence of osteoporosis while working to find a cure for the disease, and by supporting research and developing programmes of education and advocacy.
Find out more about our work at: www.osteoporosis.org.za
