How exercise and weight loss affect bone density

“I’m not fat I’m just big boned!” is a phrase we hear often. Yet, is there any truth behind it?

Today we’re going to look at how your weight affects your bone health. The impact that bodyweight and training can have on your bones hasn’t been explored enough in the fitness industry. There are several important factors that need to be taken into account in order to protect your bones.

Bone facts

When you run, the bones in the knee joint are loaded with a force of more than five times your body weight. Interestingly, bone is one of the strongest biological materials known to man. Our skeletons act in the same way as steel for buildings though our bones are alive with nerves, blood vessels and bone marrow.

Bones support the body, protect internal organs, produce red blood cells and store up to 50% of your total body minerals. Different factors can influence bone health (diet, hormones, etc.). Bones have the ability to change, and not always for the better. Those who have heard of the bone disease osteoporosis (brittle bones) will understand what I mean. Adults have around 206 bones in their body, but children actually have a much higher number. Your bones adapt to circumstances and simulations over time.

The chemical composition of bone

• 10% water
•  30% organic matter, of which 90 – 95% protein – collagen
• 60% minerals, mainly calcium and phosphorus

Together with minerals, collagen gives bones their unique structure. Collagen provides elasticity whilst the minerals give them strength.

How much do your bones weigh?

Your skeleton reaches its maximum weight between the age of 30 and 40. After this, the weight gradually decreases. Bone weight happens more rapidly for women over 50 years of age – after menopause. For this reason, women are at a much higher risk of osteoporosis.

Looking at the various sources of information, I came to the conclusion that there are many different opinions when it comes to bone weight statistics. I looked at many studies comparing the skeletons of white and black people and it was concluded that black people have about 500 to 700g heavier skeletons than white people. The skeleton of an adult white man is around 4 kg (8.8 lb), whereas an adult black man is near 5 kg (11 lb) on average. An adult white woman’s skeleton weighs around 3 kg (6.6 lb), with black women coming in at 4 kg (8.8 lb) on average.

Exercise and bone density

Partaking in physical activities helps maintain bone mass and density however, you need to place load on your bones to have an effect. Activities such as soccer, jogging or weightlifting will have a significant effect, but activities such as biking and Nordic walking aren’t as useful as they don’t load the bones as much. So, when planning your workouts, don’t forget to include movements for your bones. Paying attention to your bones early on in your life will mean you’ll live a healthier, more comfortable quality of life in your later years.

NASA (National Aeronautics and Space Administration) have also published information on the importance of bone mass. While in space, astronauts tend to lose about 1-2% of their total bone mass per month simply because of the fact that they’re not doing enough physical exercise.

However, don’t go to the other extreme and overload yourself too much, especially if you’re a woman athlete. The relationship between energy, bone mass and the menstrual cycle resulted in the term Female Athlete Triad. What does that mean? The Female Athlete Triad is a combination of eating disorder, menstrual dysfunction (amenorrhea) and decrease in bone mass. A female athlete can have one, two, or all three combinations. Usually, it happens one by one due to an athlete’s psychological factors (I am too fat) and poorly organized training regime. After restoring eating and menstruation to initial levels, bone mass won’t replenish quickly. It’s not good.

Another important aspect of bone health is maintaining a sufficient amount of calcium and vitamin D in your diet for support. However, there are differing opinions on this.

Bone health also affects the muscles. During physical activities, the bones release the active substance, osteocalcin, which helps muscles adapt to exercise.

Excess weight and bone density

Now, there is some truth behind the statement that overweight people have heavier bones. This is because as your weight increases, so does that of your bones. The bones need to become heavier in order to support a heavier load. The difference will be as little as 0.3kg (0.7 lb) to 1.5kg (3.3 lb) as opposed to 5kg (11 lb) or 10kg (22 lb).

When losing weight, you could even lose about 16.5g of bone weight per 1 kg of fat. The faster you lose weight, the faster your bone mass decreases – particularly if you’re a woman. As your bones are a vital store of minerals, this isn’t good. If you’re middle aged and want to lose weight, then you need to know it must be done slowly and wisely whatever your gender is. As pointed out above, be sure to take part in some form of physical activity that loads your bones in order to prevent any drastic change in mass.

If you have osteoporosis, then you should always consult with a doctor first and look for a solution to avoid losing further bone mass. You also need to improve balance in order to reduce the risk of falls and their impact on your bones. Below, I’ve included an image from the book Basic and Applied Biology Bone by David B. Burr and Matthew R. Allen showing the impact of being overweight on your bones. Despite the advantages having a large bone mass can have, being overweight carries far more negatives.

As you can see above, our bones are extremely complicated; maybe even more so for women. Studies also show different results even the opposite, about the impact of your weight on your bones. I wanted to give you some insight into this question.

There are many factors that can affect your bone condition. What matters is not only your lifestyle and genetics, but also your hormones. Your hormones change during weight loss and weight gain, as well as with age. All of this will have an impact on your bone mass. By choosing the appropriate training, eating a balanced diet, taking into account your individual needs and consulting with a doctor if necessary, we can certainly reduce the risk of bone disease and increase the benefits of weight loss.