Body Temperature is a day-by-day indicator of energy intake, work output, heat transfer and energy storage. Much faster than blood sugar, body weight and maximum waist circumference.

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Thermal Efficiency Of Cellular Metabolism

Human physical function is classified as a heat engine. Skeletal muscle converts chemical energy into mechanical energy and heat. Something like a gasoline engine. But all the calculations of energy from food are in units of heat given off not work performed.

A 4,000 lb car uses 1,000 calories from gasoline to move 1 mile. This is about 20% for mechanical work and 80% for heat. A 180 lb man uses 100 calories from food while moving 1 mile. This figure is the nutritional value of food and not the higher value for all contained chemical energy. Recent research has indicated that nutritional value of 100 calories to move 180 lb over a distance of 1 mile would be about 20% for physical work and 80% for heat.

We don’t really know how much energy human body cells capture from sugar and fat before energy is lost as heat. Apparently our cells have learned how to capture and transfer energy before it’s degraded into heat. Skeletal muscle appears to apply closer to 70% of energy into contraction before losing 30% as heat. Similar efficiencies function throughout the body transferring energy from one molecular form to another before energy is lost as heat.

However, the calorie intake from food eventually is lost as heat. We don’t really know how chemical and mechanical functions used energy. We do know that production, gain, transfer and loss of heat are as important to function and health as regulation of cellular metabolism. Core Body Temperature is an important indicator of health.

Circadian Rhythm Of Core Body Temperature

Core Body Temperature has a strong diurnal rhythm. The normal range of variation is about 1 degree Fahrenheit. Although the core body temperature in the evening is not affected by physical fitness, the low value before waking is decreased. The lowest point is early AM just before waking and the highest point is in the evening just before retiring for the night. Part of the change in temperature is caused by a 15% reduction in basal metabolic rate. The rest is caused by heat loss when heat is transferred by increased blood flow from the core to the skin.

As shown in the Figure, core body temperature falls during early morning hours.                                                                The comparison between awake and asleep conditions was studied in 8 young adult Caucasian men and women. All were studied for a continuous 24 hour period while lying in a temperature controlled sleep laboratory. During the Awake condition, subjects remained inactive while reading or watching videotapes. Food was given in snacks every hour. In the Sleep condition, subjects were told to go to sleep at their usual time of sleeping.

Time had a highly significant effect on temperature. Also, sleeping temperatures were lower than the corresponding hours awake.

Other studies have shown both metabolic rate and heat loss are affected. A rapid fall in oxygen consumption of about 15% occurs at the beginning of sleep. Also, skin temperature rises rapidly at the beginning of sleep and heat loss is about 10% higher.

Transition to waking has been shown to be slower.

Resting Energy Expenditure

Major efforts have measured the metabolic rates of individual organs and tissues at rest. Values of mass and oxygen consumption have been measured for 4 high-metabolic-rate organs and 3 low-metabolic rate tissues. The high-rate organs are liver, brain, heart and kidneys. The low-rate tissues are skeletal muscle, adipose tissue and all other residual organs and tissues.

The Table shows values for weight and resting energy expenditure. Measurements for these values were obtained from 131 healthy, non-obese adult men and women in Germany. Organ and tissue mass were measured using magnetic resonance imaging. The mass of each organ and tissue was determined from cross-sectional areas at several levels of tissue slices. Resting energy expenditure data were taken from files collected at the German Institute for Human Nutrition and Food Science. These data were collected from in vivo and in vitro tissue samples.

The greatest resting metabolic rates per unit of weight have been recorded from liver and brain. Skeletal muscle metabolic rate per unit weight is small but total weight is huge spread throughout the body. The remarkable feature of skeletal muscle is that energy expenditure at rest can be multiplied 10-fold during strenuous exercise.

Disrupted Circadian Rhythms

Type 2 Diabetes distorts the normal diurnal variation of body temperature. Nocturnal body temperature is markedly increased and diurnal variation is markedly diminished.

These patterns were studied in 69 men and women in Tyumen, Russia. A Control group consisted of 29 adults who were overweight with normal glucose values. The T2DM group consisted of 40 adults with abnormal FBG, HbA1c, 2-hr Glucose Tolerance and obesity. All participants kept diaries and performed self-measurements of all variables during a 24-hr study period. Oral temperature was recorded using mercury thermometers.

The Figure shows values recorded at 11 predefined times 3 hours apart. In T2DM subjects, oral temperature was higher than in Control subjects at all times except at 20:00 (8:00 pm). In addition, the normal high to low variation in temperature was wiped out. Values for fasting blood glucose measured at 6 times 6 hours apart were all greater than 5.5 mmol/l.

The continuous hyperglycemia in T2DM subjects undoubtedly caused continuous hyperinsulinemia. Consequently, an abnormally increased metabolic rate probably increased heat production throughout the 24-hr period of observation. In addition, disruption of mechanisms controlling peripheral skin blood flow probably diminished heat loss during the overnight transfer of heat from core to periphery.

Physical Activity And Body Temperature

Strenuous physical activity greatly increases body temperature. Increase in metabolic rate increases heat production while increasing physical work. Effects of fatiguing submaximal exercise for 60 minutes have demonstrated increased temperature in active skeletal muscle and core body temperature.

Effects of physical work, heat production and heat transfer have been studied in endurance-trained men living in Australia. Exercise on a bicycle ergometer was performed by 8 well-conditioned men with VO2max >50 ml/kg/min.

The Figure shows that core body temperature increased 4° Fahrenheit after 60 minutes. At the same time, temperature in leg muscles increased 8° F. Glycogen content in exercising muscle decreased by more than 50%.

Range of Circadian Rhythm is Increased by physical fitness. This has been studied in young men living in England. A group of 7 men who were physically fit according to reports of leisure-time activity were compared to another group of 7 men who were physically inactive. Although the core body temperature in the evening was not affected by physical fitness, the low value before awakening was decreased.

Calorie Restriction And Circadian Rhythms

Calorie restriction is well known to decrease total metabolic rate. Enough so that many people report that substantial reductions in calorie intake have little effect on their body weight. Less is known about its effect on Circadian Rhythm of Core Body Temperature.

This has been studied. The effects of calorie restriction for 6 months was studied in 46 men and women living in Louisiana. One group of 12 had 25% calorie restriction and another group of 12 had 12.5% calorie restriction and structured exercise. Both of these two groups had weight reduction of -10% by 24 weeks of intervention. Both groups also had significant decreases in fasting plasma insulin levels.

The Figure shows both groups had significant reductions in core body temperature. Also, both groups had significant reduction in day temperature.

However, only the group who combined calorie restriction with exercise had significant reduction in early morning body temperature.

These results suggest that calorie restriction reduced metabolic rate all day and night while exercise plus calorie restriction also increased nocturnal heat loss.

Summary

You should know your body temperature before and after a good night’s sleep just like you know your height, weight and maximum waist circumference.

• measure your fasting oral temperature and its range from the evening before.
• measure your oral temperature before and immediately after 30 minutes of the most strenuous exercise you can do for that time. Then check it again 2 or 3 hours later.

If your fasting oral temperature is more than 98° Fahrenheit and its range from 12 hours the night before is less than 1° F your average insulin level is too high.

• to reduce levels of insulin and improve your health, you should increase your physical activity and decrease your calorie intake.
• your maximum waist circumference should be no more than 40% of your standing height.

If your fasting blood sugar without medication is more than 100 mg/dL there are several things you should do.

• increase your skeletal muscle mass.
• increase your pedometer steps/min.
• decrease your daily calorie intake.

Measuring your fasting body temperature and its range from the evening before is a convenient and accurate way to follow your progress towards reversing type 2 diabetes and preventing its recurrence.

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