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    Summer Reading: The Story of the Human Body: Evolution, Health, and Disease

     

    While this book isn't "light" reading, it is really fascinating and easily digestible.  Written by an evolutionary biologist, Lieberman uses a lens of science, history, culture and evolution to understand the state of health and disease. He tackles subjects such as:

    1. The influence of hunter gatherer lifestyle on physical evolution of the body (they had no cavities, were taller than farmers, and walked miles to acquire smaller numbers of calories),

    2. The energy/caloric requirements went up as our brains got bigger (and so hunter gatherers had to walk even longer distances to get the calories they needed to sustain life), 

    3. Our bodies were made to store fat to have energy readily available when food is scarce (doesn't help us now that food is NOT scarce),

    4. "Diet and physical activity are far more potent predictors of obesity and illness" than genes,

    5. Stress/cortisol response was a necessary strategy to keep people safe in cave man times, but now that same stress/cortisol causes a host of diseases...

    6.

    was tremendous, from 1 mile in earlier caveman times to 6...and now we wonder why obesity is such a high rate in the US and yet many adults can barely get 10,000 steps per day in their daily life.

     

    The "mismatch" diseases that occur...those diseases that are caused by the lifestyle we live not matching up with our human biology is the reason for many of the diseases of today eg cancer, obesity, cardiovascular disease. We wonder why obesity is at such a high rate in the US and worldwide, when many adults and children can't meet the recommended 10,000 steps per day to maintain their health. Our bodies make cortisol for our high stress situations, that are not really life or death stress. Cortical responses put us in perpetual states of adrenal stress, building in time and causing us disease. We do not have a high enough physical activity level and in fact even active lifestyles today are sedentary compared to a century ago. Our bodies were made to move and our energy/caloric requirements do not equal the calories we expend.

     

    What can you do? Make healthy lifestyle choices for yourself, in terms of physical activity and nutrition.  As a physical therapist, we are in a position to make lifestyle suggestions that can have a huge impact on the physical and mental health of the children that we work with. These changes could have a profound impact on many of the public health issues we face today.

     

    Future blogs are going to review some important studies on physical activity and the intensity of physical activity needed to make changes in health. Coming soon to a theater near you :)

     

    Favorite quotes:

     

    "First, cortisol causes you not only to release glucose but also to crave calorie-rich food (this is why stress makes you yearn for comfort food). 38 As you now know, both responses elevate your insulin levels, which then promote fat storage, especially in visceral fat, which is about four times more sensitive to cortisol than subcutaneous fat. 39 To make matters worse, constantly high levels of insulin also affect the brain by inhibiting its response to another important hormone, leptin, which fat cells secrete to signal satiety. As a result, the stressed brain thinks you are starving, so it activates reflexes to make you hungry while simultaneously activating other reflexes to make you less active. 40 Finally, as long as the environmental causes of stress remain (your job, poverty, commuting, and so on), you keep on secreting too much cortisol, which then leads to too much insulin, which then increases appetite and decreases activity. Another vicious circle is sleep deprivation, which is sometimes caused by elevated levels of stress, hence high levels of cortisol, but which then increases cortisol. Insufficient sleep also elevates levels of yet another hormone, ghrelin. This “hunger hormone” is produced by your stomach and pancreas and stimulates appetite. Numerous studies find that people who sleep less have higher ghrelin levels and are more likely to be overweight. 41 Apparently, our evolutionary history did not adapt us well to cope with relentless, endless stress and sleep deprivation. We also were never adapted to be physically inactive, but the relationship between exercise and obesity is often misunderstood, sometimes grievously so. If you were to leap up right now and jog three miles, you’d burn about 300 calories (depending on your weight). You might think that these extra spent calories will help you lose weight, but numerous studies have shown that regular moderate to vigorous exercise leads only to modest reductions in weight (typically 2 to 4 pounds). 42 One explanation for this phenomenon is that burning an additional 300 calories a few times a week amounts to a relatively small number of calories compared to your body’s overall metabolic budget, especially if you are already overweight. What’s more, exercise stimulates hormones that temporarily suppress appetite but also stimulate other hormones"

     

    "And boy have our environments changed in more ways than diet. As noted in chapter 9, one major realm of change is that we are more stressed and we sleep less—two related factors that contribute to weight gain in pernicious ways. The word “stress” has negative connotations, but stress is an ancient adaptation to save you from dangerous situations and to activate energy reserves when you need them. If a lion roars nearby, a car nearly runs you over, or you go for a run, your brain signals your adrenal glands (which are on top of your kidneys) to secrete a small dose of the hormone cortisol. Cortisol doesn’t make you stressed; it is released when you are stressed. Among its many functions, cortisol gives you needed, instant energy: it causes your liver and fat cells, especially visceral fat cells, to release glucose into the bloodstream, it increases your heart rate and increases your blood pressure, and it makes you more alert and inhibits sleep. Cortisol also gets you ready to recover from stress by making you crave energy-rich foods. All in all, cortisol is a necessary hormone that helps keep you alive. Stress, however, has a dark and fattening side when it doesn’t abate. One of the problems of chronic, long-term stress is that it elevates cortisol levels for extended periods of time. Many hours, weeks, and even months of too much cortisol is harmful for many reasons, not the least of which is by promoting obesity through a vicious circle that works as"

     

    "The final and most important point about adaptation is really a crucial caveat: no organism is primarily adapted to be healthy, long-lived, happy, or to achieve many other goals for which people strive. As a reminder, adaptations are features shaped by natural selection that promote relative reproductive success (fitness). Consequently, adaptations evolve to promote health, longevity, and happiness only insofar as these qualities benefit an individual’s ability to have more surviving offspring. To return to an earlier topic, humans evolved to be prone to obesity not because excess fat makes us healthy, but because it increases fertility. Along the same lines, our species’ proclivities to be worried, anxious, and stressed cause much misery and unhappiness, but they are ancient adaptations to avoid or cope with danger. And we not only evolved to cooperate, innovate, communicate, and nurture, but also to cheat, steal, lie, and murder. The bottom line is that many human adaptations did not necessarily evolve to promote physical or mental well-being."

     

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