DR MEGAN ROSSI: The secret to healthy bones? You can’t beat onions!

Bone is an amazing material — weight for weight, it’s actually as strong as steel. Well, healthy bone is, but weakened bone can break with the force of a simple sneeze.

Yet few people think about their bone health until they have a fracture or a scan which identifies a weakness.

However, it really is something we should all pay more attention to, as weak bones can ultimately rob you of your independence, and in many cases there are really simple diet and lifestyle adjustments (including eating onions!) that can help prevent future problems. And these are things I think everyone should be doing from a young age, even in your 20s.

Bone is a living thing: old bone is constantly being broken down and replaced with new bone (our skeleton is completely replaced over a decade).

But from quite a young age — after the age of 30 — we lose more than we make, meaning we experience a progressive loss of bone mass, a process which in women accelerates after the menopause.

For those with osteoporosis the process is accelerated even more, and their bones can become so weakened that even a minimal knock, a sudden move or sneeze can lead to a fracture.

This is still incredibly common — according to the Royal Osteoporosis Society, more than three million people in the UK have osteoporosis (and it’s more common in women).

The risk of osteoporosis hinges on multiple factors, including genetics and taking certain medications such as steroids, which can slow the production of new bone.

But diet can play a part, too, and many people with osteopenia, the precursor to osteoporosis when the bone is starting to weaken, may prevent the progression to full-blown osteoporosis by switching to a more bone-friendly diet.

The one thing we can all do for our bones is to have calcium-rich food in two meals a day.

For those with osteoporosis the process is accelerated even more, and their bones can become so weakened that even a minimal knock, a sudden move or sneeze can lead to a fracture

Around 99 per cent of bone is formed of calcium — it helps mould the strength and structure. If your diet doesn’t provide enough calcium for your body’s needs (it’s also required, for example, to help your heart contract, digestive enzymes to work, your blood to clot and your nervous system to function), then it will be leached from your bones, weakening them.

But the pathways through which calcium is absorbed can become saturated, like a bottleneck on a busy road. So if you have a single, calcium-rich meal containing more than 500 mg (the amount in a large glass of milk), your body will absorb much less of it than if you consume small quantities across the day.

So what are the best sources? Milk, yoghurt, good-quality cheese and sardines are fantastic. The sardine bones are especially rich in calcium.

I also eat the ends of chicken wings: I crisp them up in the oven for a delicious and calcium-rich snack, with two providing 400 mg or so of the 700mg of calcium we need daily.

Those on a plant-only diet need to be more savvy.

Spinach and rhubarb provide calcium but they also contain oxalates, compounds that bind to the calcium, meaning it isn’t so easily absorbed. The same mechanism is why foods such as nuts, seeds and wholegrains containing phytates are also not considered good calcium sources. However, tofu set in calcium (it will say on the packet), broccoli, kale and spring greens are decent sources. But if your diet is plant-based, I’d recommend having calcium-enriched, plant-based milks, too.

Bone health isn’t all about calcium. You also need adequate vitamin D, as several of the transporters that carry calcium across our gut lining rely on vitamin D to work; having sufficient vitamin D increases the absorption of calcium by around 50 per cent.

Now to explain about onions. These are a type of prebiotic — like garlic, legumes, artichokes, dates and barley — which act as fertiliser, feeding the gut bacteria which make the gut slightly more acidic, an environment that makes calcium more absorbable.

Prebiotics may also help bone health in other ways. Gut bacteria break them down to produce short-chain fatty acids, which in animal studies have been shown to help regulate the osteoclasts (the cells responsible for breaking down bone) and bone mass.

Onions specifically contain the flavonoids quercetin and kaempferol, thought to stimulate osteoblasts (the cells that generate new bone).

A 2009 study published in the journal Menopause found that women over the age of 50 who consumed onions once or more a day had better bone density than those who consumed onions once a month or less.

The researchers suggested that women who ate onions daily could reduce their risk of hip fracture by more than 20 per cent versus those who never consume onions. I’m not saying onions are bone ‘super‑food’, but research does suggest they can play an important supporting role (and baked with olive oil and a chopped date, they are irresistible — see my recipe, above).

Exercise is also good for bones, specifically weight-bearing or high-impact exercise as it exerts force that encourages the cells to form new bone in response. This includes running, brisk walking, aerobics or tennis, but even climbing the stairs can help. Meanwhile, watch out for the bone saboteurs. One of the worst (aside from smoking, which slows the activity of the osteoblasts) is crash dieting.

Diets providing fewer than 1,000 calories per day can lower bone density, and research by the University of Colorado in the U.S. found that bone loss resulting from weight loss was not reversed when weight was regained.

So if you’re trying to lose weight, opt for the slow and steady strategies that also tend to result in better long-term weight maintenance. And when you do diet, keep eating sources of calcium and protein.

Finally, let me bust a myth — the idea that fizzy water will pull calcium from your bones is not backed by science. In fact, you might want a glass to wash down your crunchy chicken tips.

Did you know?

Most people know that chocolate is toxic for dogs. It’s due to a chemical called theobromine, which increases heart rate and dilates blood vessels. Dogs can’t break this chemical down, so its effects are heightened, and the darker the chocolate, the more theobromine — and the more risk for dogs. 

AskMegan 

My mother has kidney problems, especially high potassium levels. Are there any foods to improve kidney function and reduce potassium (or foods to avoid)?

James Law

Potassium is found in a range of foods, and it’s important for maintaining a regular heartbeat, among hundreds of other functions.

Normally your kidneys control your potassium levels, irrespective of what you eat. Unfortunately, if they’re not working well, you need to monitor your potassium intake.

Many healthy foods such as avocado, banana, pulses, potatoes and natural yoghurt, are high in potassium. But that doesn’t mean your mum should completely cut these out — some cooking techniques, for instance double-boiling your potatoes (i.e. boil, replace the water, and boil again), leach out some of the potassium of certain vegetables, which may be a way for your mum to still enjoy them regularly.

She should instead focus on avoiding sources of potassium that are otherwise nutrient-poor, such as crisps, milkshakes and processed meats. But it’s important she’s referred to a renal (kidney) dietitian who can help develop a meal plan personalised to her needs and level of kidney function.

Try this: Halloumi sprout canape

Not big on Brussels sprouts? This recipe with caramelised onions will change your mind — and it provides the perfect hit of prebiotics for you and your gut this Christmas.

Makes 15 cocktail sticks

• 15 Brussels sproutsl
• ½ tbsp extra-virgin olive oil
• 80g halloumi, cut into 5 slices
• 1 tbsp wholegrain mustard
• 15 cocktail sticks

For the caramelised onions:

• 1 tbsp extra-virgin olive oil
• 150g red onion, thinly sliced
• 1 tbsp balsamic vinegar
• 1 Medjool date, made into a paste (using back of a spoon and 2 tbsp of boiling water) or 1 tbsp sweetener of choice

Preheat the oven to 200c/180c fan/gas mark 6. Line a baking tray with baking paper.

Toss sprouts in the olive oil and season, then spread on tray and bake for 12 to 15 minutes, or until just cooked and starting to change colour.

Meanwhile, prepare the caramelised onions by heating a tablespoon of olive oil over a medium heat in a frying pan.

Add onion, balsamic vinegar and date paste. Cook for 15 minutes, stirring frequently until sticky and caramelised.

In a small frying pan over a medium heat, fry the halloumi for one minute on each side until golden.

To assemble, cut each slice of halloumi into three pieces. Cut each sprout in half. Place one half on each cocktail stick, add some onion, then a piece of halloumi, then a little more onion, a drop of mustard, and top with the other half of the sprout.