Today I want to talk with you about two critical connections between body fat and knee health. The first of them is well known, but often underestimated. The second one is little known and poorly understood. Let’s start with number one: the increased load on your joints.
Body Fat Fact 1: Obvious, but Underestimated
The more you weigh, the higher the load your joints have to handle. But – and this is the important point many people don’t realize – if you gain 10 pounds, the additional load on your knees will not just be 10 pounds. Depending on what you’re doing, the excess load in the knee could be up to 90 pounds! This is because whenever we’re moving, forces much greater than that of our own bodyweight act on the joints.
Cleather et al. found that when jumping, the load at the patellofemoral joint (the one between your kneecap and your thighbone) is between 2.4 and 4.6 times your bodyweight. It’s even higher at the joint between your tibia and your femur (6.9 – 9.0 times your bodyweight) and highest at the ankle (8.9 – 10 times bodyweight).
Some of you might argue that you don’t jump, but consider the research findings of Kutzer and colleagues: even when you’re just walking on a level surface, the peak resultant forces on the knee are 261% of your bodyweight and I think it’s safe to say that we all walk around every now and then.
For the sake of argument, let’s assume a person gains 5 pounds of body fat and walks 5,000 steps per day. That’s 2,500 steps with one leg at an additional load of 13 pounds (5 x 261%). In other words, that person’s knees have to deal with 32,500 pounds of additional load per day!
All of a sudden that small five pound difference becomes huge and it’s very easy to see how even such a seemingly irrelevant amount of body fat can have an impact on the health of your knees.
Please understand that I’m not saying five pounds of flab will ruin your knees. What I am trying to tell you is that five pounds can make a difference and you’d be very smart to take it seriously, especially since there’s another fact to bear in mind when it comes to body fat.
5 pounds make a huge difference in the course of one day
Body Fat Fact 2: Little Known and Poorly Understood
When I was teenager, I used to think of body fat as some sort of passive storage system that the human body uses to save unneeded calories for later use. The reality is a lot more complicated.
Excess body fat is so much more than energy storage. It will also manipulate your hormone levels and secrete pro-inflammatory substances! The following is a very brief summary of these two dangers.
Excess body fat causes inflammation
Once your body starts to carry excess fat, you will slowly shift into a state of low-level chronic inflammation. Inflammation is the body’s response to an injury and normally disappears once the injury has healed, the inflammation caused by excess body fat, however, is chronic.
Chronic low-level inflammation has been associated with a host of diseases ranging from autoimmune disorders (e.g., asthma, rheumatoid arthritis) over psychological diseases (e.g., depression, bipolar disorder) to cognitive problems (e.g., ADD, dyslexia). You can see why this topic is very important for everyone, regardless of whether they have knee pain.
The connection between excess body fat and increased inflammatory markers has been well established through research studies. It’s something you need to deal with as soon as you realize it, because the effects are subtle and will creep up on you silently.
Excess body fat will upset your hormone levels
Body fat manipulates your hormone levels by secreting leptin and estrogen. Put simply, leptin regulates how hungry you feel and how much energy your body expends. Estrogen, on the other hand, is an important sex hormone.
For optimal health, we require our hormonal system to be balanced. Having too much leptin is as bad as not having enough leptin and the same holds true for estrogen and other hormones (yes, men need some estrogen too). Problems arise when this balance is disturbed, as is the case when you carry excess body fat.
Stored body fat elevates your leptin levels, trying to signal satiety to your brain. The more body fat you have, the higher the leptin levels. However, chronically elevated levels of leptin also increase your risk of developing leptin resistance.
A useful analogy is how your hearing adapts to noise: the more noise there is the less sensitive your hearing will be and the louder a certain message has to be delivered. More leptin equals the satiety message being delivered at a higher volume and at some point, your leptin receptors will get used to that higher volume (i.e., higher circulating levels of leptin). Leptin resistance has developed.
With leptin resistance, more leptin is needed to deliver the message (“Stop eating!”) to your brain, which means you eat more to feel full, even though you don’t need to. Since your body has no use for these additional calories, some of them will be stored as body fat and so the vicious circle continues.
Body fat also secretes estrogen. In men, excess estrogen makes building muscle more difficult, increases risk for prostate enlargement, lowers sex drive, increases body fat, and contributes to infertility. In women, excess estrogen worsens symptoms of PMS and elevates risk for breast cancer, to name just two effects.
You need to take action!
As you can see, the danger being overweight puts you in is very real. If you or someone you know faces this problem, you need to take action.
I have to admit that I’m not the best person to talk to when it comes to losing weight. I’ve been thin for all of my life and I actually was underweight until I started strength training. If you want to lose body fat, you should talk to someone who has done exactly that.
Cleather, Daniel J.; Goodwin, Jon E.; Bull, Anthony M. J. (2013): Hip and knee joint loading during vertical jumping and push jerking. In Clin Biomech (Bristol, Avon) 28 (1), pp. 98–103.
Kutzner, I.; Heinlein, B.; Graichen, F.; Bender, A.; Rohlmann, A.; Halder, A. et al. (2010): Loading of the knee joint during activities of daily living measured in vivo in five subjects. In J Biomech 43 (11), pp. 2164–2173.