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To Maintain Bone Health, These Key Nutrients Can't Be Ignored in Plant-Based Diets

Milk and alternatives
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Key Takeaways:

  • Poorly planned plant-based diets may fall short on meeting protein, calcium, and vitamin D needs, which can have negative effects on bone health.
  • A new study shows that switching from a mostly animal-based to a mostly plant-based diet can be detrimental to bone health if the new diet lacks these nutrients.

When people think about foods for bone health, dairy products often come to mind. Years of marketing by the dairy food industry remind us that calcium and vitamin D from milk are essential bone-building nutrients.

Yet, sales of cow’s milk have declined in recent years, and sales of plant-based beverages have increased. Almond milk is the most popular, followed by soy, coconut, and oat-based beverages.

But do these drinks offer the same bone-building nutrients as cow’s milk?

A new study published in The Journal of Nutrition looked at how three dietary patterns with differing levels of plant-based foods may affect bone and mineral metabolism in healthy adults. They found that switching from animal proteins to plant-based alternatives carried added risks to bone health if the proper nutrients were not accounted for.

The Rise of Plant-Based Foods

As more people turn to plant-based foods and beverages for nourishment, scientists wonder how it will affect our overall health.

Previous studies have shown that plant-based diets have more fiber and less saturated fat, so they help prevent heart disease and type 2 diabetes.

But what about the health of our bones? If we step away from dairy and other animal-based proteins, will we still get enough protein, calcium, and vitamin D to support bone health?

Bones are living tissue made of collagen, which contains a matrix of proteins, minerals, and vitamins. This structure allows bones to grow and repair themselves.

Bones are constantly being remodeled. Bone breakdown and destruction is called resorption. In childhood, bone formation outpaces bone resorption. But as we age, bone resorption exceeds bone formation.

Our goal as adults is to keep bones strong and slow bone resorption with a proper diet and weight-bearing physical activity (as well as medications as needed).

A bone-protective diet needs to provide the nutrients that are required to build and repair bones, which include protein, calcium, vitamin D, phosphorus, vitamin K, and magnesium. These can come from animal or plant-based food sources. 

Some past prospective studies on plant-based diets show that they are fine for bone health as long as they provide adequate nutrients, including calcium and vitamin D.

Getting enough protein is vital for healthy bones. Previous meta-analyses shown no differences between protein from animal vs. plant sources and their effect on bone mineral density.

What Did the Study Find?

The study was a 12-week clinical trial with 136 adults, who were randomly assigned to follow one of three diets with 17% of calories from protein:

  1. The “animal” diet: 70% animal protein and 30% plant-based protein
  2. The “50/50” diet: 50% animal protein and 50% plant-based protein
  3. The “plant” diet: 30% animal protein and 70% plant-based protein

Note: None of the diets were fully plant-based or vegan.

The researchers found that the groups who partially replaced animal proteins with plant-based proteins for 12 weeks showed increased markers of bone resorption and formation.

Verywell spoke with Dr. Suvi Itkonen, an adjunct professor at the University of Helsinki in Finland and one of the investigators on this study, to explain these results.

“We found that both bone formation and resorption were higher in the plant-based protein diet vs. the animal protein-based diet,” says Itkonen. “This means accelerated bone turnover, which may in the long term be detrimental to bone health.”

She also said that calcium and vitamin D intakes were lower in the plant vs. animal diet in this particular group of participants.

It’s assumed that the changes in bone metabolism and the lower intake of calcium and vitamin D were caused by the low amount of dairy products consumed.

“The results could be different if fluid dairy products had been replaced with plant-based drinks fortified with vitamin D and calcium,” says Itkonen.

“We chose unfortified products because during the study time they were the most common ones, and the fortified products may have confounded the findings.”

The study participants were not using vitamin or mineral supplements during the study period, which would also account for the low intake of calcium and vitamin D.

This study design does not represent what bone health may be for people on plant-based diets who choose fortified beverages and use vitamin supplements.

Dr. Suvi Itkonen

It is important to focus on what you are removing from your diet and what you are adding there. If you decrease the amount of milk, which is a good source of calcium and vitamin D, you have to think from where you’ll get those nutrients in your diet.

— Dr. Suvi Itkonen

Better Bone Health

Falling short of protein, calcium, and vitamin D can be problematic for bones. If the diet is low in protein, adults are at a higher risk of bone fractures. Protein plays a role in preventing bone loss, acquiring new bone, and maintaining overall bone health.

If the diet is low in calcium, the body borrows calcium from bones for your blood and tissues, where it’s needed to do other jobs. This can cause bones to become brittle and porous, and lead to low bone mass and osteoporosis.

If the diet lacks vitamin D, it leads to decreased calcium absorption and higher parathyroid hormone concentrations, which are linked to increased bone loss.

Calcium and Vitamin D

Properly planned diets can provide a variety of nutrients from many foods, whether they are plant- or animal-based.

“It is important to focus on what you are removing from your diet and what you are adding there,” says Itkonen. “If you decrease the amount of milk, which is a good source of calcium and vitamin D, you have to think from where you’ll get those nutrients in your diet.”

Pamela Fergusson, RD, PhD, is a plant-based dietitian and consultant in Nelson, British Columbia. She recommends her plant-based clients have one or more daily servings of a fortified plant-based beverage to get enough calcium and vitamin D.

“The rest of their calcium requirement can be met through whole plant foods,” says Fergusson. “Calcium-set tofu, kale, and tahini are good sources, but calcium is found in many plant foods, including most beans, greens, nuts, seeds, and dried fruits.”

Fergusson also recommends 400-800 IU vitamin D supplements (depending on age), especially for people living in areas that have cold climates.

“Although some plant-based products, just like dairy, are fortified with vitamin D, data show that many North Americans are at risk of deficiency, and relying on fortified products alone is likely insufficient,” says Fergusson. 

Itkonen adds that it is important to follow the recommended supplementation doses, because studies have shown that high vitamin D doses do not seem to give extra benefit to bone health.

Pamela Fergusson, PhD, RD

Although some plant-based products, just like dairy, are fortified with vitamin D, data show that many North Americans are at risk of deficiency, and relying on fortified products alone is likely insufficient. 

— Pamela Fergusson, PhD, RD

Get Enough Protein

In addition to calcium and vitamin D, it’s vital to get enough protein. Low-protein diets (less than 0.8 g/kg body weight/day) are often seen in patient with hip bone fractures.

Diets too high in protein (more than 2.0 g/kg body weight/day) are also not recommended for bone health, especially when calcium levels are low.

Animal-based protein sources include meat, poultry, seafood, dairy, and eggs. For plant-based options, Fergusson recommends soy foods, beans, lentils, meat alternatives, nuts, and seeds.

“Soy is a complete protein, meaning it contains all essential amino acids," says Fergusson. "Some people avoid soy including tofu, soy milk, tempeh, and edamame unnecessarily due to fear mongering, but soy is actually healthy and [a] good source of protein for vegans, vegetarians, and anyone looking for plant-based alternatives to meat.”

Phytic Acid

People who eat lots of beans and grains on a plant-based diet may hear warnings about phytic acid, which is often called an “anti-nutrient.”

Fergusson explains that phytic acid can bind to calcium and create phytates, which reduce mineral absorption.

“Phytic acid is reduced by rinsing, soaking, sprouting, fermenting, and cooking grains and beans,” says Fergusson. “As phytic acid does not completely block nutrient absorption, the best advice for plant-based eaters is to ensure high intakes of minerals like iron, zinc, and calcium, knowing that some portion of their intake will be blocked."

What’s Next For This Area of Study?

Itkonen will continue to explore the science of bones and diet patterns.

“It would be interesting to study diets where the amounts of calcium and vitamin D are balanced but the sources of protein are different,” says Itkonen. “This approach would enable us to catch the possible effects of animal and plant proteins on bone.”

Itkonen’s next research project is about partial replacement of red and processed meat with legumes, and she hopes to analyze the effects on bone turnover.

 

What This Means For You:

If you cut back on animal-based foods in favor of a plant-based diet, ensure you still get adequate protein, vitamin D, and calcium intake to support bone health. Choose fortified milk alternatives, soy foods, beans, lentils, nuts, and seeds to get a wide range of bone-supporting nutrients.

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