The disproven acid-ash hypothesis claims that a diet rich in animal proteins (containing acid-forming minerals) causes the reduction of the blood pH (making it more acidic). Therefore, it forces the bones to leach minerals in order to buffer the increased acidity, leading to osteoporosis.
However, milk and other dairy products are proven to be especially beneficial for our bones, since they are a great source of bone health-promoting nutrients, such as calcium, protein, vitamin D, phosphorus, zinc and magnesium. (1, 2)
High calcium intake has proven to be a very effective buffer in diets high in acid-forming foods (read more..)
In order to disprove the acid-ash hypothesis, studies done specifically on dairy products, including supplements, show that dairy is beneficial for bone health rather than causing bones to lose minerals.
Here are some of the main results of these studies:
- A twelve months study showed that the rate of bone mineralization increased in young girls whose primary calcium sources came from dairy products. (3)
- A three year study on 30-42 year old premenopausal women showed that, an increase of the dietary calcium, from dairy products, by 610mg per day, did not result in a vertebral bone loss in comparison to about 3% loss in those not on the extra dairy calcium diet. (4)
- A two year study on postmenopausal women revealed that milk powder supplementation reduced the bone density loss. The best results were obtained when supplementation is accompanied with physical exercise. (5)
- Calcium absorption improves in postmenopausal women who are on a low calcium diet when the intake of dietary proteins is increased from 10%-20% of energy.
Animal proteins, including those from milk sources, did not have a negative effect on the calcium balance. (6)
The hypothesis (often used by some vegans and paleo enthusiasts) that consumption of dairy products is harmful through increasing acidity in our bodies has been proven wrong. (7)
Proteins (whether from animal or vegetarian sources) with an adequate supply of vitamin D and calcium, are essential ingredients for the bone formation and the prevention of osteoporosis.
There is no evidence that the protein from vegetarian sources has a better effect than from animal sources on the calcium metabolism, minerals bone loss or rate of bone fractures. (8)
A 12 year prospective study involving 77,761 women revealed that drinking a high amount of milk per day (two or more glasses as advised by many official sources) has not decreased the risk of bone fractures in comparison to women who drank only 1 glass per day.
This study showed that it is not necessary to drink a very high amount of milk in order to protect your bones. (9)
Balanced dairy, dietary calcium and exercise is the key.
NOTE: although consumption of milk and milk products in general proves to have many health benefits, including bone health, it should be taken in moderation like any other food.
In addition to the obvious reasons to avoid or limit milk due to milk protein allergies or high lactose intolerance, consumption of high amounts of milk and milk products may have negative health effects. (read more..)
Some studies actually show the association between excessive milk consumption and acne and prostate cancer.
NUTRITION FACTS VS NUTRITION MYTHS
You will find a summary of the most common nutrition myths and evidence-based nutrition facts here.