Tag Archives: Basal metabolic rate

All Wound Up

Our body wants to eat, sleep and work at specific times. Scientists now know what makes the biological clock tick, writes T.V. Jayan

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All living organisms — humans are no exception — are controlled by a master clock. This biological timepiece, located in the brain, aligns an organism’s biological, behavioural and physiological activities with the day and night cycle. Its tick tock wakes us up in the morning, reminds us to eat at regular intervals and tells us when to go to bed.

But what sets this internal timekeeping, known as the circadian rhythm, has remained a mystery for long. This, despite scientists having had clues about its existence for more than a century.

The puzzle is slowly unfolding, thanks to advances in modern biology that offer a better insight into genes and their workings. Scientists now know the exact location of the master pacemaker and how is it regulated.

Research has also shown the circadian rhythm shares a reciprocal relationship with metabolism. In other words, while the circadian rhythm can influence metabolic activity, food intake can also modulate the functioning of the biological clock.

The mechanism by which feeding modulates the components of the clock machinery was discovered last month by a team of researchers led by Gad Asher of the University of Geneva. The paper, which appeared in the latest issue of Cell, shows that a protein called PARP-1 is at play here. The scientists found that mice that lack the gene that secretes PARP-1 fail to give the correct food intake cues to the circadian clock, thereby disrupting the synchronisation.

“This is an important finding,” says Raga Krishnakumar, a University of California San Francisco University researcher who, together with her former mentor W. Lee Kraus, showed early this year that PARP-1 is a multi-faceted protein that also regulates the expression of another protein which plays a vital role in aging, apart from helping contain DNA damage.

Scientists believe disruptions in the synchronisation between the circadian rhythm and metabolism play a key role in triggering many disorders that plague the modern world such as obesity, diabetes and cardiovascular diseases.

The master clock occupies a tiny area in the hypothalamus region of the brain. Called the suprachiasmatic nucleus (SCN), this brain region — the size of a grain of rice — contains a cluster of nearly 20,000 neurons. These neurons, in response to light signals received from the retina, send signals to other parts of the brain as well as the rest of the body to control a host of bodily functions such as sleep, metabolism, body temperature and hormone production.

As per the cues received through these neurons from the master clock, the cellular clocks in the tissues in different body organs are reset on a daily basis. The operation of these cellular clocks is controlled by the co-ordinated action of a limited number of core clock genes.

The year 1994 was a watershed year in research on the circadian rhythm. American Japanese scientist Joseph Takahashi, working at Northwestern University in the US, discovered the genetic basis for the mammalian circadian clock. The gene his team discovered was named CLOCK in 1997. Subsequently, scientists discovered several other genes associated with the timekeeping function such as BMAL1, PER and CRY, which are also involved in the working of the main SCN clock machinery as well as subsidiary clocks in other parts of the body.

The cues received from the master clock are important. Based on them, various genes in the cells change their expression rhythmically over a 24-hour period. It times the production of various body chemicals such as enzymes and hormones so that the body can function in an optimal fashion.

In the normal course, the body follows the master clock in setting its physiological and psychological conditions for optimal performance. While the 24-hour solar cycle is the main cue for resetting the master clock — just like a wall-mounted clock resets after a 24-hour cycle — there are other time cues as well: food intake, social activity, temperature and so on. “Unlike geophysical time, the biological clock does not follow an exact 24-hour cycle on its own. Various external and internal time cues that it receives play a vital role in bringing the periodicity close to 24 hours,” says Vijay Kumar Sharma of the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, who has been studying the circadian rhythm for years.

However , modern society often imposes deviations from the regular work-rest cycle. “Basically, mammals including humans are diurnal (active during the day rather than at night). Whatever be the external compulsions (night shifts or partying late), the inner mechanisms of the body follow a diurnal pattern,” says Sharma. “It is bound to be out of sync if we deviate from the routine.”

“A major consequence of modern lifestyle is the disruption of the circadian rhythm. This leads to a number of pathological conditions, including sleep disturbances, depression, metabolic disorders and cancer. Studies reveal the risk of breast cancer is significantly higher in industrialised societies, and that the risk increases as developing countries become more and more westernised. Moreover, a moderate increase in the incidence of breast cancer is reported in women working nightshifts,” says Sourabh Sahar, a researcher working on the circadian rhythm at the University of California, Irvine.

Need more proof that the body has a mind of its own?

Source: The Telegraph (Kolkata, India)

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Do the Math & Lose the Weight

Using simple formulas, a calculator and helpful websites, you can determine how much to eat and exercise.

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To lose weight, calculate the calories you need to consume based on your age and gender — then factor in how many you actually burn.

It isn’t difficult, requiring little more than a calculator. The equations produce numbers that fit the population average, so consider them only a starting point.

The simplest way to calculate calorie needs is to multiply current weight by 11 through 15, which gives a range of calories needed to maintain that weight.

So a 150-pound woman who wants to stay at that weight would need to eat 1,650 to 2,250 calories. Why the difference? If her activity level is high (exercising vigorously every day), she can eat more because she’s burning more. If she wants to lose weight, she’s going to have to cut calories.

Because a pound of fat equals about 3,500 calories, cutting 500 calories a day will mean one pound lost in a week, a reasonable amount. But eating less isn’t the only way to slim down. To cut 500 calories a day, you can also cut calories by 250 and do a workout that burns 250 calories.

A more accurate calorie assessment can be done using the Harris Benedict Equation, developed in 1919, which starts with basal metabolic rate to calculate calories needed to maintain weight.

What the equation doesn’t take into consideration is lean muscle mass. Someone with a lot of muscle and little body fat will need more calories, and those with higher body fat will need less. As fitness levels increase, so does BMR.

Kara Mohr, co-owner of a Louisville, Ky.-based nutrition and fitness facility, says that since these numbers are based on averages, some calorie tweaking may be necessary to find the right formula. If weight doesn’t drop after a few weeks, cut the calories, increase the exercise, or both. Always hungry? Add calories or back off on the workouts.

Calorie counts for various foods can be found online at sites such as CalorieKing.com and TheCalorieCounter.com, and calories burned via various activities can be found at CaloriesPerHour.com and NutriStrategy.com

Click to see:->Counting calories is a tough math problem

Sources Los Angrles Times

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Childhood Obesity

Definition:Obesity is defined as an excessive accumulation of body fat. Obesity is present when total body weight is more than 25 percent fat in boys and more than 32 percent fat in girls (Lohman, 1987). Although childhood obesity is often defined as a weight-for-height in excess of 120 percent of the ideal, skinfold measures are more accurate determinants of fatness (Dietz, 1983; Lohman, 1987).

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A trained technician may obtain skinfold measures relatively easily in either a school or clinical setting. The triceps alone, triceps and subscapular, triceps and calf, and calf alone have been used with children and adolescents. When the triceps and calf are used, a sum of skinfolds of 10-25mm is considered optimal for boys, and 16-30mm is optimal for girls (Lohman, 1987).

A few extra pounds do not suggest obesity. However they may indicate a tendency to gain weight easily and a need for changes in diet and/or exercise. Generally, a child is not considered obese until the weight is at least 10 percent higher than what is recommended for the height and body type. Obesity most commonly begins in childhood between the ages of 5 and 6, and during adolescence. Studies have shown that a child who is obese between the ages of 10 and 13 has an 80 percent chance of becoming an obese adult.

Causes:
The causes of obesity are complex and include genetic, biological, behavioral and cultural factors. Basically, obesity occurs when a person eats more calories than the body burns up. If one parent is obese, there is a 50 percent chance that the children will also be obese. However, when both parents are obese, the children have an 80 percent chance of being obese. Although certain medical disorders can cause obesity, less than 1 percent of all obesity is caused by physical problems. Obesity in childhood and adolescence can be related to:

* poor eating habits
* overeating or binging
* lack of exercise (i.e., couch potato kids)
* family history of obesity
* medical illness (endocrine, neurological problems)
* medications (steroids, some psychiatric medications)
* stressful life events or changes (separations, divorce, moves, deaths, abuse)
* family and peer problems
* low self-esteem
* depression or other emotional problems

As with adult-onset obesity, childhood obesity has multiple causes centering around an imbalance between energy in (calories obtained from food) and energy out (calories expended in the basal metabolic rate and physical activity). Childhood obesity most likely results from an interaction of nutritional, psychological, familial, and physiological factors.

* The Family

The risk of becoming obese is greatest among children who have two obese parents (Dietz, 1983). This may be due to powerful genetic factors or to parental modeling of both eating and exercise behaviors, indirectly affecting the child’s energy balance. One half of parents of elementary school children never exercise vigorously (Ross & Pate, 1987).

* Low-energy Expenditure

The average American child spends several hours each day watching television; time which in previous years might have been devoted to physical pursuits. Obesity is greater among children and adolescents who frequently watch television (Dietz & Gortmaker, 1985), not only because little energy is expended while viewing but also because of concurrent consumption of high-calorie snacks. Only about one-third of elementary children have daily physical education, and fewer than one-fifth have extracurricular physical activity programs at their schools (Ross & Pate, 1987).

* Heredity

Since not all children who eat non-nutritious foods, watch several hours of television daily, and are relatively inactive develop obesity, the search continues for alternative causes. Heredity has recently been shown to influence fatness, regional fat distribution, and response to overfeeding (Bouchard et al., 1990). In addition, infants born to overweight mothers have been found to be less active and to gain more weight by age three months when compared with infants of normal weight mothers, suggesting a possible inborn drive to conserve energy (Roberts, Savage, Coward, Chew, & Lucas, 1988).

Complecations:
There are many risks and complications with obesity. Physical consequences include:

* increased risk of heart disease
* high blood pressure
* diabetes
* breathing problems
* trouble sleeping

Child and adolescent obesity is also associated with increased risk of emotional problems. Teens with weight problems tend to have much lower self-esteem and be less popular with peers. Depression, anxiety, and obsessive compulsive disorder can also occur.

Treatment :
Obese children need a thorough medical evaluation be a pediatrician or family physician to consider the possibility of a physical cause. In the absence of a physical disorder, the only way to lose weight is to reduce the number of calories being eaten to increase the child’s or adolescent’s level of physical activity. Lasting weight loss can only occur when there is self-motivation. Since obesity affects more than one family member, making healthy eating and regular exercise a family activity can improve the chances of successful weight control for the child or adolescent.

Obesity treatment programs for children and adolescents rarely have weight loss as a goal. Rather, the aim is to slow or halt weight gain so the child will grow into his or her body weight over a period of months to years. Dietz (1983) estimates that for every 20 percent excess of ideal body weight, the child will need one and one-half years of weight maintenance to attain ideal body weight.

Early and appropriate intervention is particularly valuable. There is considerable evidence that childhood eating and exercise habits are more easily modified than adult habits (Wolf, Cohen, Rosenfeld, 1985). Three forms of intervention include:

1. Physical Activity

Adopting a formal exercise program, or simply becoming more active, is valuable to burn fat, increase energy expenditure, and maintain lost weight. Most studies of children have not shown exercise to be a successful strategy for weight loss unless coupled with another intervention, such as nutrition education or behavior modification (Wolf et al., 1985). However, exercise has additional health benefits. Even when children’s body weight and fatness did not change following 50 minutes of aerobic exercise three times per week, blood lipid profiles and blood pressure did improve (Becque, Katch, Rocchini, Marks, & Moorehead, 1988).

2. Diet Management

Fasting or extreme caloric restriction is not advisable for children. Not only is this approach psychologically stressful, but it may adversely affect growth and the child’s perception of “normal” eating. Balanced diets with moderate caloric restriction, especially reduced dietary fat, have been used successfully in treating obesity (Dietz, 1983). Nutrition education may be necessary. Diet management coupled with exercise is an effective treatment for childhood obesity (Wolf et al., 1985).

3. Behavior Modification

Many behavioral strategies used with adults have been successfully applied to children and adolescents: self-monitoring and recording food intake and physical activity, slowing the rate of eating, limiting the time and place of eating, and using rewards and incentives for desirable behaviors. Particularly effective are behaviorally based treatments that include parents (Epstein et al., 1987). Graves, Meyers, and Clark (1988) used problem-solving exercises in a parent-child behavioral program and found children in the problem-solving group, but not those in the behavioral treatment-only group, significantly reduced percent overweight and maintained reduced weight for six months. Problem-solving training involved identifying possible weight-control problems and, as a group, discussing solutions.

Obesity frequently becomes a lifelong issue. The reason most obese adolescents gain back their pounds is that after they have reached their goal, they go back to their old habits of eating and exercising. An obese adolescent must therefore learn to eat and enjoy healthy foods in moderate amounts and to exercise regularly to maintain the desired weight. Parents of an obese child can improve their children’s self esteem by emphasizing the child’s strengths and positive qualities rather than just focusing on their weight problem.

When a child or adolescent with obesity also has emotional problems, a child and adolescent psychiatrist can work with the child’s family physician to develop a comprehensive treatment plan. Such a plan would include reasonable weight loss goals, dietary and physical activity management, behavior modification, and family involvement.

Resources:
http://www.lipsychiatric.com/common-disorders.asp#obe
http://www.kidsource.com/kidsource/content2/obesity.html