Is eating natto good for your bones?
Eating natto regularly is associated with less bone density loss and fewer fractures in postmenopausal women, most likely due to its high vitamin K2 content. Whether this applies equally to men or people of other backgrounds has not been well studied.
In a long-running study of more than a thousand Japanese women, those who ate at least seven packs of natto per week after menopause had a 44% lower chance of suffering an osteoporosis-related fracture than women who ate little or no natto. This link held up after the researchers accounted for bone density and other factors. Eating fewer than seven packs per week also showed a lower risk, but that difference was not statistically convincing.
The key appears to be vitamin K2, also known as menaquinone-7. Natto is by far the richest dietary source of this vitamin. Eating natto measurably raises vitamin K2 levels in the blood and encourages the body to produce osteocalcin, a protein needed to build bone tissue. In men aged 65 and older, the link between natto and better bone density disappeared as soon as researchers factored in vitamin K2 levels, strongly suggesting that the vitamin K2 in natto is the active ingredient.
Tofu and other soy products did not show this bone-protective effect in the same studies. This is most likely due to fermentation: the Bacillus subtilis bacteria that make natto produce large amounts of vitamin K2 that are barely present in ordinary soy. Natto also contains unique compounds that form during fermentation and, in animal studies, slowed bone breakdown, though it has not yet been tested whether these substances work the same way in people.
All of the large studies have been conducted in Japanese populations. A combined analysis of five studies that followed people over time confirmed the protection against fractures in Asian women, with the strongest effect seen in women in early menopause. Whether the same applies to people of other backgrounds who start eating natto has not yet been studied. In men, the link was not clear in that combined analysis.
This answer draws on two large long-running studies in postmenopausal Japanese women, a cross-sectional study in older Japanese men, a combined analysis of five studies that followed people over time, and a small study in people that confirmed the vitamin K2 mechanism. The protection against fractures and bone density loss is fairly consistent in (post)menopausal Asian women, but all of this research maps associations rather than proving cause and effect. Animal studies involving compounds from natto are included only to illustrate a possible mechanism and say nothing yet about effects in people. The evidence for men and for non-Asian populations is limited.
Is eating plant-based bad for your bones?
Eating strictly vegan is associated with lower bone density, but if you adequately supplement calcium and vitamin D, the elevated fracture risk largely disappears. As a vegan, also pay attention to vitamin B12, and discuss any supplement use with your GP or dietitian.
Does bone broth actually do anything for your bones?
Animal and laboratory research shows positive signals, but there are no studies in humans. If you want to protect your bones, focus on calcium, vitamin D, and exercise, as those are the options backed by human evidence.
Is soy good or bad for your bones after menopause?
Soy isoflavones probably do not protect the bones of postmenopausal Western women in any clinically meaningful way. It is better to focus on proven measures such as adequate calcium, vitamin D and exercise.
Do carbonated drinks damage your bones?
Regularly drinking large amounts of sugary carbonated drinks is associated with lower bone density, especially in women and during puberty. Moderate consumption appears less harmful, but it is preferable to replace soft drinks with beverages that support bone development.
Does drinking a lot of alcohol weaken your bones?
Chronic heavy drinking demonstrably weakens your bones and substantially raises the risk of a hip fracture; for your bones there is no safe level above two drinks per day.
Can having too little body fat damage your bones?
Too little fat can damage your bones, but muscle mass and the location of fat matter at least as much. If you have concerns about bone health in combination with low body fat, discuss this with your general practitioner or sports medicine physician.