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What You Should Know About Meat and Osteoporosis
There is a complex relationship between protein intake and osteoporosis. While proteins are needed to drive bone development and maturation, high protein diets can reduce bone mineral density. However, studies show that there is a difference between the effects of plant proteins and animal proteins on bone mineral density. What makes high protein and meat consumption bad for the bones? How are vegetable proteins better than animal proteins for the lowering the risk of osteoporosis? And what about studies that insist high protein intake is good for the bones? Read on to find out the answers to these questions.
by Brad Chase
Epidemiological studies provided the first indication that the amount of proteins consumed may influence the risk of osteoporosis.
Most of these studies found that people who consumed high-protein diets for long periods were more prone to bone fractures later in life than those who consumed far less proteins.
This does not mean that protein is bad for your bones. On the contrary, protein makes up one third of your bone mass. Therefore, while calcium is the most abundant micronutrient in the bone, protein is the most abundant structural macronutrient.
In addition, some studies show that protein improves the absorption of calcium. However, increased absorption of calcium does not directly translate to higher bone mineral density.
Just as high intake of calcium does not make the bone stronger, higher consumption of proteins does not improve bone strength. In addition, high protein consumption may be just as bad for your bones in the same way as high dose calcium supplementation is bad for your health.
But how does protein increase the risk of osteoporotic fracture? Simply, by raising the acidity of the blood.
Beyond their roles in maintaining the structural integrity of the bones, calcium and proteins are also essential to the maintenance of acid-base balance in the blood.
The pH of the blood needs to be kept within a narrow range. Therefore, if it strays too much into the acidity or alkalinity range, normal biochemical functions are severely affected.
Therefore, by raising blood acidity, high protein diets can cause metabolic acidosis, a state of increased blood acidity. To counteract this abnormal state, the body raises alkalizing agents such as the calcium.
This means that calcium and protein are both important to the acid/base balance because proteins are acidifying while calcium is an alkalizing agent.
Therefore, the body recruits the calcium stored in bones to neutralize the increased blood acidity caused by high protein diets. The calcium stripped from the bones binds to acidic protein metabolites and chaperones them through the body to prevent damage to organs and tissues.
Unfortunately, the bound calcium is excreted along with the acidic protein metabolite it binds to.
When this occurs over a long period of time, there is a progressive loss of calcium from the bones.
While some researchers have suggested that calcium supplementation along with high protein diets may prevent demineralization, studies have shown that bone mineral density falls steadily in those who consumed high protein diets even when they were placed on calcium supplements.
Most people believe that consuming more proteins can promote muscle development and general health but the truth is that after the body meets its daily need of protein, the rest is simply discarded.
Unlike carbohydrates and fats, excess dietary protein is not stored.
The body burns excess protein as immediate energy and not to bulk up muscles. Unfortunately, the process of breaking down protein raises the acid load of the body.
First, excess protein is broken down into its constituent amino acids. Since amino acids are rich in nitrogen and sulfur, they form different inorganic acids very easily when they are further broken down. Without a corresponding high intake of magnesium and potassium to neutralize these metabolites, the increased acidity can interfere with the normal biochemical processes of the body.
To prevent damage to organs and tissues, the body then moves calcium from the bones to neutralize the increased acid load.
Therefore, high protein diets are needless. They do not improve health any more than diets containing normal amounts of proteins. Besides, they can demineralize the bones and set off other adverse reactions in the body by causing metabolic acidosis.
All proteins increase the acid load of the blood and studies show that the amount of acidic metabolites excreted in the urine is directly linked to the protein content of the diet consumed.
However, when compared to plant proteins, animal proteins produce the highest acidic components in the urine.
In addition, proteins with the highest proportion of amino acids that contain sulfur increase blood acid level the highest. Such amino acids include cysteine and methionine. And animal proteins have more of these sulfur-containing amino acids than plant (vegetable) proteins.
Besides having lower sulfur-containing amino acids and producing lesser acid load than animal proteins, plants also contain alkalis in the form of potassium and magnesium salts.
Potassium and magnesium are alkalizing minerals that can help neutralize the acidity of plant proteins.
Therefore, plant as a source of protein is a lot gentler on the bones. It not only serves as a readily available source of protein but it also provides alkalizing minerals to prevent the leaching of calcium from bones.
To investigate the protection offered by potassium for bones, researchers demonstrated that potassium salts such as potassium citrate and potassium bicarbonate prevented calcium loss and maintained bone mineral density even when protein consumption was not lowered.
The advantage of plant protein over animal protein was also proven by epidemiological studies that show that the incidence of osteoporosis was lower among vegans (and people who eat diets rich in vegetables rather than meat and dairy) than the general population that largely consumed animal proteins especially meats.
Such studies also showed that countries known for their high vegetable diets have low rates of osteoporosis.
Therefore, even though people in these countries consume high protein diets, they usually consume little animal protein while the magnesium and potassium in their vegetables neutralize the acidity of plant proteins.
Researchers from the University of California and Western Human Nutrition Research Center collaborated for a 10-month study to determine the effect of plant protein and animal protein on bone growth.
For their study, they recruited 48 healthy women aged 18 – 40 years. Over the course of the study, some of the participants ate only plant foods (vegans) while the others ate plant and animal foods (omnivores). By taking blood and urine samples, the researchers measured the different markers of bone health.
The results of the study showed that
This study provides an alternative view of the effect of protein consumption on the bone. It demonstrated that animal proteins raised blood acid levels and increased calcium loss more than plant proteins.
However, the study also indicates that animal proteins increase the risk of osteoporosis not because they promote calcium loss from the bones but because they reduce the formation new bones.
Even though this study suggests that animal proteins do not increase bone calcium loss from bones, it is important to note that what the results show is that animal proteins do not increase calcium loss from bones any more than plant proteins.
This means that proteins (whatever the source) increase calcium loss from bones.
However, people who consume more plant proteins are more likely to replace the old bones lost (resorption) with new bones.
There is still an open debate in the medical community over the effect of high protein intake, especially meat consumption, on bone health.
The key points raised by those who believe high protein intake can increase the risk of osteoporosis are discussed above. This section examines some of the studies often quoted by experts who argue that meat consumption and high protein diet are good for the bones.
The Framingham Osteoporosis Study is commonly used to determine the effect of diet, drugs and supplements on the risk of osteoporosis. A 2000 study published in the Journal of Bone and Mineral Research took some of its data to determine the effect of dietary protein on the risk of osteoporosis among the elderly.
By comparing dietary protein intake to changes in bone mineral density in 391 women and 224 men over a period of 4 years, the researchers found that low protein intake was linked to increased risk of bone fractures.
The researchers also showed that the participants who ate higher animal proteins did not experience poor bone health.
While this study seems to suggest that higher protein intake is good for health, it is important to understand what it actually says. The population of this study was the elderly and previous studies have established that malnutrition was common among the elderly.
Therefore, high protein intake is desirable for the elderly to improve bone health and also to improve muscular strength.
A 1997 study published in the journal, Osteoporosis International, identified that malnutrition is a risk factor for osteoporotic bone fracture in the elderly. Malnutrition causes bone loss, muscle wasting and impaired movement coordination. Therefore, it increases the odds of the kinds of fall that cause bone fractures.
This means higher protein intake (even high meat consumption) may help old people improve muscle strength and bone mineral density.
One way in which proteins may provide these benefits is by raising the production of insulin-like growth hormone (IGF-1).
Most of the studies that have found high protein intake good for bone health involved the elderly.
Such studies include the 2010 paper published in the journal, Current Opinion in Clinical Nutrition and Metabolic Care as well as a 2008 paper published in The American Journal of Clinical Nutrition.
Curiously, all of these studies concluded with the recommendation that the high protein diet given to old people must be taken with sufficient calcium intake and fruits and vegetables.
The researchers recommended calcium for mineralizing the bones while fruits and vegetables for alkalizing the acidic breakdown products of proteins. Therefore, they recognized the acidifying effect of high protein diets and its negative effect on bone mineral density.
The observed benefits of high protein intake does not even persist as we age. It seems that the benefits of increased protein intake on bone strength is quickly overshadowed by its negative effects the older we get.
A 2004 study published in the Journal of Bone and Mineral Research correlated protein intake with incidence of hip fractures in 1,167 participants and 1,334 controls recruited from 18 Utah hospitals over a period of 5 years.
The results of the study found that higher protein intake was associated with reduced risk of hip fracture in old people between the ages of 50 and 69 years. However, no such protection was observed for those aged 70 – 89 years.
There are also studies that indicate that high protein diets and meat consumption does not affect bone mineral density in postmenopausal women. One of such studies was published in 2003 in The Journal of Nutrition.
The researchers first acknowledged that increased consumption of purified proteins (protein-only diets) can lower calcium levels in the body. However, they believed controlled high protein diets may be beneficial for these women.
Therefore, they detailed the differences between two groups of women placed on calcium-rich diets but with one group placed on high meat diets while the other ate low meat diets.
The researchers found that calcium retention was the same between the 2 groups over the period of 8 weeks. They also noted that the high renal acid excretion in the high meat group reduced over time.
They concluded that under controlled conditions, high meat diets did not increase urinary calcium loss or affect markers of bone metabolism.
It should be noted that there is not much difference between the protein contents (12% vs. 20%) of both the high meat and low meat groups in this study. Therefore, it is unlikely that the effects of both diets on bone health will differ significantly.
In addition, bone mineral density was not actually measured and the urinary calcium loss reported is not a true indication of the calcium content of the bone.
Other such studies have reached similar conclusions. A 1995 study published in The American Journal of Clinical Nutrition showed that high meat consumption did not affect calcium status but may increase zinc levels and reduce iron levels.
However, a 2001 study published in the same journal served as a reminder of the difference between animal protein and plant protein with regards to the risk of osteoporotic bone fractures.
In a study involving 1,035 postmenopausal women over the age of 65 years, the researchers correlated protein intake data with X-ray measurements of bone mineral density.
The results of the study showed that the women who took more vegetable proteins than animal proteins had significantly lower risks of bone loss in their femurs and also reduced risk of hip fractures than the women who consumed more animal proteins than vegetable proteins.
This study provides support for the view that vegetable proteins produce lesser acid load on the body and also provide minerals that can protect the bone from calcium loss.
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