Nutritional Value of Bone Gristle

Chomping down on a piece of rubbery, flavorless bone gristle while enjoying a juicy steak can turn you off meat altogether. People typically don't eat gristle, and it's nutritional value hasn't been assessed. But it may offer health benefits similar to collagen, another type of connective tissue.

That juicy steak you enjoy fresh off the grill is made up of different types of protein, including muscle tissue and connective tissue. Muscle tissue is comprised of many fibers bundled together by connective tissue, which provide structure and support.

The two most abundant connective tissues in meat are collagen and elastin. Collagen surrounds individual muscle tissues and groups of muscle tissues, and is found in the tendons connecting muscle to bone.

Elastin is a heavier connective tissue that also surrounds muscle groups and forms a covering called silverskin. Silverskin, that pearlescent membrane you see on some meat, separates muscle groups and tendons that connect the muscle group to bone. Elastin is the type of connective tissue known as bone gristle.

The particular cooking method, along with the amount of connective tissue, both collagen and elastin, affects the tenderness of cooked meat. Collagen breaks down to gelatin when cooked with moist heat and actually makes the muscle tissue more tender. Elastin does not break down when cooked, which is why it remains stringy, chewy and gristly. It is typically removed from cuts of meat before they reach the consumer, although there may be some in bone-in meat.

Read more: Are Collagen Supplements Safe?

Like the muscle tissue it surrounds, connective tissue is rich in protein. When the protein content of meat is measured, connective tissue protein — primarily collagen — is included in the total. For example, according to the USDA, a 3-ounce cut of top sirloin has 25 grams of protein, some of which comes from the collagen. The elastin content may or may not be included, depending on whether it has been removed.

Proteins, including connective tissue, are rich sources of amino acids, which your body uses to make proteins that support many functions in the human body. Meat provides the full spectrum of the essential amino acids — the ones your body can't make and you need to get from food. These include:

• Histidine
• Isoleucine
• Leucine
• Lysine
• Methionine
• Phenylalanine
• Threonine
• Tryptophan
• Valine

Dietary protein also provides the nonessential amino acids. Your body can make these from the essential acids you consume as well as the breakdown of body proteins that is a normal biological process. The nonessential amino acids are:

• Alanine
• Arginine
• Asparagine
• Aspartic acid
• Cysteine
• Glutamic acid
• Glutamine
• Glycine
• Proline
• Serine
• Tyrosine

Your body needs amino acids to make all proteins, including collagen. Collagen is the most abundant type of protein in the human body. As in animal meat, it provides support and structure — it basically holds the body together.

There are several types of collagen in the body, but the most common are types I, II and III. Type I collagen is the most abundant kind and is required for bones and teeth. It is also one of the main proteins in skin and contributes to its firmness and elasticity. With age, collagen production slows, which leads to aging skin that is dry and wrinkled. Exposure to sunlight, cigarette smoke and pollution can accelerate collagen loss.

Type II collagen is a part of elastic cartilage which provides support to joints. Decreased collagen can lead to stiffness and a loss of flexibility in tendons and ligaments, according to Cleveland Clinic. It may also result in joint pain and the development of osteoarthritis, a condition that causes a deterioration of the cartilage that protects and provides cushioning around the ends of bones.

Type III is found in arteries, organs and muscles. Low levels of collagen may lead to muscle loss and weakness.

So you might wonder — does eating the collagen in meat translate to increased collagen in your bones, skin, muscles and other tissues? Not directly. Your body can't absorb collagen in its whole form, according to registered dietitian Alyssa Pike. Your body has to break down collagen into amino acids or chains of amino acids called peptides.

In addition to age, a poor diet can lead to collagen loss, according to the Cleveland Clinic. You can't turn back time, but you can make sure to get plenty of the nutrients your body needs to make collagen. Amino acids from the protein in animal foods — fish, meat, chicken, eggs and cheese are rich sources. But you can also get amino acids from protein in plant foods.

Most plant-based sources of protein, including beans and whole grains, are called incomplete proteins because they are low in or missing at least one amino acid. For example, beans are low in tryptophan and methionine. However, other plant foods contain sufficient amounts of those amino acids. Assuming you eat a variety of foods, a plant-based diet can provide all the amino acids your body needs for healthy collagen production.

Vitamin C is also required for your body to synthesize collagen. A deficiency in this nutrient causes impaired collagen production and weakened connective tissues, which can result in joint pain and poor wound healing, among other ill effects. Other nutrients involved in collagen production include the essential minerals zinc and copper.

Read more: 13 Surprising Vegetarian Sources of Protein

Recent years have seen increased interest in boosting collagen due to its benefits for skin and joints, and collagen supplements have flooded the market. Manufacturers make many claims about supplemental collagen's ability to improve skin appearance and joint health, but so far there is little scientific evidence to back up these claims.

Some small studies have had promising results. One study published in the Journal of the International Society of Sports Nutrition in October 2013 found that 120 days of supplementation with type II collagen from chicken sternum increased knee joint extension in 55 subjects who experienced joint pain when exercising, compared to placebo. It also showed potential to reduce or eliminate knee pain compared to a placebo, but results were not statistically significant.

In another study published in Nutrition Research in September 2018, participants who consumed a supplement for 90 days containing fish collagen and other nutrients, including vitamins and antioxidants, saw improvements in skin elasticity and joint function compared to a group taking a placebo. However, there is no way to know if the positive results were from the collagen or from the other nutrients in the supplement — or a combination of both.

Until there is more evidence for benefits of collagen supplementation, you're likely better off investing in high-quality protein sources, fresh fruits and vegetables for vitamin C and whole grains for zinc and copper.