It seems like it should be simple: Just exercise to burn more calories and reduce your calorie intake.
A dramatic example of the challenges of maintaining weight loss comes from a recent National Institutes of Health study. The researchers followed 14 contestants who had participated in the "World's Biggest Loser" reality show. During the 30 weeks of the show, the contestants lost an average of over 125 pounds per person.
Why is it so hard to lose weight and keep it off? Weight loss often leads to declines in our resting metabolic rate -- how many calories we burn at rest, which makes it hard to keep the weight off.
So why does weight loss make resting metabolism go down, and is there a way to maintain a normal resting metabolic rate after weight loss? As someone who studies musculo-skeletal physiology, I will try to answer these questions.
Activating muscles deep in the leg that help keep blood and fluid moving through our bodies is essential to maintaining resting metabolic rate when we are sitting or standing quietly. The function of these muscles, called soleus muscles, is a major research focus for us in the Clinical Science and Engineering Research Center at Binghamton University. Commonly called "secondary hearts," these muscles pump blood back to our heart, allowing us to maintain our normal rate of metabolic activity during sedentary activities.
Resting metabolic rate (RMR) refers to all of the biochemical activity going on in your body when you are not physically active. It is this metabolic activity that keeps you alive and breathing, and very importantly, warm.
Quiet sitting at room temperature is the standard RMR reference point; this is referred to as one metabolic equivalent, or MET. A slow walk is about two MET, bicycling four MET, and jogging seven MET. While we need to move around a bit to complete the tasks of daily living, in modern life we tend not to move very much. Thus, for most people, 80 percent of the calories we expend each day are due to RMR.
There's no question that eating a balanced diet and regular exercise are good for you, but from a weight management perspective, increasing your resting metabolic rate may be the more effective strategy for losing weight and maintaining that lost weight.
Metabolic activity is dependent on oxygen delivery to the tissues of the body. This occurs through blood flow. As a result, cardiac output is a primary determinant of metabolic activity.
The adult body contains about four to five liters of blood, and all of this blood should circulate throughout the body every minute or so. However, the amount of blood the heart can pump out with each beat is dependent on how much blood is returned to the heart between beats.
If the "plumbing" of our body, our veins in particular, was made of rigid pipes, and the skin of our legs was tough like that of bird legs, cardiac outflow would always equal cardiac inflow, but this is not the case. The veins in our body are are quite flexible and can expand many times their resting size, and our soft skin also allows lower body volume expansion.
As a result, when we are sitting quietly, blood and interstitial fluid (the fluid which surrounds all the cells in our body) pools in the lower parts of the body. This pooling significantly reduces the amount of fluid returning to the heart, and correspondingly, reduces how much fluid the heart can pump out during each contraction. This reduces cardiac output, which dictates a reduced RMR.
A much more convenient approach to maintaining RMR during and after weight loss is to train up your secondary hearts, or soleus muscles. The soleus muscles are deep postural muscles and so only require low-intensity, but long-duration, training.
Alternatively, if squatting or long-duration balance exercises do not fit into your lifestyle, passive exercise devices will stimulate those muscles as you sit are available. (Full disclosure: Binghamton University has licensed technology to a company, which I have shares in and consult for, to commercialize such a device.) The concept here is that specific mechanical vibrations can be used to activate receptors on the sole of the foot, which trigger a postural reflex arc, which in turn causes the soleus muscles to undergo reflex contractions.
Kenneth McLeod is entrepreneur in residence and director of the Clinical Science and Engineering Research Laboratory at Binghamton University, State University of New York. A version of this story appeared on The Conversation.
Originally posted here:
Why your weight loss plateaus, and how to fight it - CNN.com
