What makes you fat?

 A recent editorial in the journal Obesity addressed common misconceptions about obesity. The author covered twenty-two points. Number nine was particularly interesting:  “Although less obvious than the fact that energy intake must be equal to energy expenditure, weight stability also requires that the substrate mixture oxidized must be equivalent, on average, to the composition of the nutrient mix consumed.”

Put another way, over any extended period of time, during which one’s weight and body composition (percent fat, muscle, etc.) are stable, the amount of carbohydrate, protein and fat “burned” by metabolism must be equal to the amounts of these nutrients consumed in the diet.

This has practical implications. If one consumes a diet high in fat, one must also metabolize fat at the same average rate. There are three common ways that fat metabolism is stimulated:

  1. exercise
  2. depletion of the body’s glycogen (carbohydrate) stores
  3. increase in the body’s fat stores.

Therefore, under any constant set of conditions, including exercise/activity and eating habits, one’s percent body fat will be a reflection of the amount of fat in the diet.

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Are you an “Active Couch Potato” ?

A review article published last year in the journal Exercise and Sport Sciences Reviews discussed the medical hazards of prolonged sitting.  The authors point out that changes in transportation, building standards, communications, entertainment technology, and workplace practices, have combined to significantly reduce demands for physical activity.

They propose, with supporting epidemiological evidence, that prolonged sitting is a distinct health risk factor from too little exercise and, furthermore, that breaking up sedentary time can provide health benefits.

Even adults who meet the recommended exercise guidelines of thirty minutes per day may be sedentary for prolonged periods during the day.  An example would be someone who exercises vigorously every morning before going to work in an environment that requires sitting for hours at a time.  According to the authors, such “Active Couch Potatoes” showed significant detrimental effects on their waist circumference (an indicator of % body fat), blood pressure, plasma glucose levels, triglycerides and HDL cholesterol.

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Sleep and Teenagers!

Two recent studies published in the Journal of Clinical Sleep Medicine highlight the importance of adequate sleep in teenagers. Both studies evaluated the effect of school start times.

In one study, conducted in Israel, the start of the school day was delayed by one hour for one week. A control group did not have their day delayed. After one week the eighth-grade students in the experimental group performed significantly better on two different tests of attention.

In the other study, motor vehicle crash statistics from a pair of neighboring communities in Virginia with different high-school start times were compared. The community with the earlier school start times (by approximately seventy-five minutes) had significantly more teen automobile accidents. This is consistent with an earlier study, also published in the Journal of Clinical Sleep Medicine, in which a one hour delay in high school start times was associated with a decline in teen crashes.

A limitation of these studies is that sleep per se was inferred but not measured. They do, however, illustrate the kind of practical changes that can lead to real improvements in health, safety, and performance.

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