A short-term keto diet is unlikely to harm healthy adults’ bones if it includes enough calcium, vitamin D, protein and vegetables, but there are reasons for caution over the long term. Strict keto can be low in calcium-rich foods if you cut back on dairy, and it removes many fruits, beans and whole grains that provide potassium and magnesium. In a small study in elite race walkers, three and a half weeks of a very low-carb, high-fat diet increased a blood marker of bone breakdown and lowered markers of bone building around exercise. Children on long-term medical ketogenic diets are routinely monitored for bone health. If you have osteoporosis or a high risk of it, talk to your doctor before starting keto.
What bones need
Bone is living tissue that is constantly broken down and rebuilt. Peak bone mass is reached in early adulthood, and bone density slowly declines afterward, faster in women after the menopause. The NHS recommends three main things to keep bones strong: enough calcium and vitamin D, regular weight-bearing and strength exercise, and avoiding smoking and heavy drinking.
| Nutrient | Why it matters | Keto-friendly sources |
|---|---|---|
| Calcium | The main mineral in bone | Cheese, Greek yogurt, milk (in your carb allowance), canned sardines and salmon with bones, almonds, kale, broccoli, calcium-set tofu |
| Vitamin D | Helps absorb calcium | Sunlight, oily fish, eggs, fortified foods, supplements |
| Protein | Part of the bone matrix | Fish, eggs, meat, dairy, tofu |
| Magnesium | Involved in bone formation | Nuts, seeds, leafy greens, avocado, dark chocolate |
| Vitamin K | Helps bone proteins work | Leafy greens, broccoli, cabbage |
| Potassium | Helps balance acid in the body | Avocado, spinach, mushrooms, zucchini |
Adults need 700 mg of calcium a day, according to the NHS, and should consider a 10 mcg vitamin D supplement in autumn and winter.
How keto might affect bones
Fewer calcium-rich foods
Some people on keto cut out milk and yogurt because of their lactose content. Hard cheese is low in carbs and rich in calcium, so it fits well, but people who avoid dairy entirely need to plan other sources.
Changes in bone turnover
In the race walker experiment, the low-carb diet raised CTX, a marker of bone breakdown, and lowered P1NP and osteocalcin, markers of bone building, both at rest and after exercise, compared with a high-carb diet. These are short-term blood markers in athletes training very hard, not measurements of bone density or fractures, so it’s not clear what they mean for most people. They do suggest that combining very low carbs with intense training and a low energy intake could be hard on bones.
Low energy intake
Eating too little, whether on keto or any other diet, is one of the biggest risks to bone health, especially for women and athletes. It can stop periods and lower estrogen, which protects bones. Our guide to keto for women explains the warning signs.
Fewer fruits and vegetables
Diets rich in fruit and vegetables are linked with better bone health, possibly because of their potassium, magnesium and vitamin K. Strict keto limits fruit but can include plenty of low-carb vegetables, which helps.
Children on medical ketogenic diets
Children treated with long-term ketogenic diets for epilepsy can grow more slowly and may have lower bone density. That’s why their diets are supplemented and monitored closely by specialist teams. Our guide to keto for children covers this.
What about protein and acid?
An old idea suggested that high-protein diets make the body more acidic and leach calcium from bones. More recent evidence shows that adequate protein is good for bones, especially when calcium intake is also adequate. A keto diet with moderate protein and plenty of vegetables isn’t a problem for most people on this front.
How to protect your bones on keto
- Include calcium-rich foods daily: cheese, Greek yogurt, sardines with bones, almonds, leafy greens and calcium-set tofu.
- Get enough vitamin D, from sunlight in summer and a supplement in winter.
- Eat plenty of non-starchy vegetables for magnesium, potassium and vitamin K. Our list of keto vegetables has options.
- Eat enough overall. Avoid very large calorie deficits, especially with heavy training.
- Do strength and weight-bearing exercise at least twice a week.
- Keep alcohol moderate and don’t smoke.
- Get checked if you have risk factors for osteoporosis, such as a family history, early menopause, long-term steroid use or a previous fracture.
Who should be more careful?
- Postmenopausal women and older adults, who already lose bone faster.
- People with osteoporosis or osteopenia.
- Athletes, especially women, combining keto with high training loads.
- Anyone with a history of eating disorders.
- Children and teenagers, who are still building bone.
For these groups, a moderate lower-carb or Mediterranean-style diet may be a safer way to improve weight and blood sugar. Our guide to keto for older adults explains the other risks after 60.
Common questions
Does keto cause osteoporosis?
There’s no good evidence that keto causes osteoporosis in healthy adults, but long-term effects aren’t well studied, and some people are at higher risk.
Should I take calcium supplements on keto?
Try to get calcium from food first. If you can’t, ask your doctor or pharmacist whether a supplement is right for you.
Is cheese enough for calcium on keto?
Hard cheeses are rich in calcium: 30 g of cheddar has about 210 mg. Combined with other sources, it can help you reach 700 mg a day. Our guide to whether cheese is keto compares cheeses.
Do I need dairy on keto for strong bones?
No, but it helps. Without dairy, plan other calcium sources every day, such as canned sardines or salmon with bones, calcium-set tofu, almonds, kale and fortified unsweetened plant milks.
Safety note: Keto isn’t suitable for everyone. If you have diabetes, kidney or liver disease, take regular medication, or are pregnant or breastfeeding, talk to your doctor before cutting carbs this far (why it matters).
This article is general information, not medical advice. Talk to your doctor or a registered dietitian before making big changes to how you eat, especially if you have a health condition, take regular medication, or are pregnant or breastfeeding.
