Obesity is the biggest health challenge worldwide. WHO global estimates show that about 13% of the world’s adult population(11% of men and 15% of women) were obese in year 2014, with roughly doubling up of obese population from 1980 to 2014. Obesity is not only a problem of developed nations, but also is a major health concern for developing nations as well. In developing countries with emerging economies, the rate of increase of childhood obesity and overweight has increased 30% more than that of developed nations.
Obesity is a lifestyle disorder, which not only imposes severe restrictions on quality of life, but also increases risk of multiple diseases like diabetes, cardiovascular disorders (like Stroke and heart attacks), and certain cancers as well.
One can find all kinds of advice and tips to loose weight, which do not have any scientific basis. Trying to loose weight, without understanding the physiology behind it is like driving blindly, and may even harm you. Equipped with the right information, and understanding the underlying physiology can help you set up reasonable goals and have realistic expectations.
What is obesity?
Obesity is a state of excessive fatty (adipose) tissue mass in the body. In common parlance it is considered equivalent to increased body weight. This is not true, as increase in muscle or bony density, as seen in athletes may cause more weight even in lean individuals.
Who is considered obese, and overweight?
Body mass index(BMI)
is widely used to define overweight and obesity. BMI is weight/height2 (in kg/m2). A BMI of 30 is most commonly used as a benchmark for obesity in both men and women. Overweight is the term used to describe individuals with BMIs between 25 and 30. A BMI between 25 and 30 should be considered significant as the risk of all kinds of complications associated with obesity increase in individuals with BMI of more than 25.
However, taking BMI as a parameter has drawbacks too, as it is not a direct measure of fatty tissues in the body. Other methods that can be used to assess obesity are skin fold thickness, and underwater weighing.
Waist to hip ratio(WHR)
is another and more scientific way of defining obesity. It represents the fat mass around the waist. It is simply measured as the ratio of circumference at the waist, usually just above the belly button, and the hip circumference at its widest part of the buttocks. To more accurately take the measurements as defined by WHO, the waist circumference should be taken midway between the lowest palpable rib and top of iliac bone, and the hip circumference is to be taken parallel to floor at the widest portion of the buttocks.
As per WHO standards, a WHR of more than 0.85 in females and 0.90 in males is an defines abdominal obesity.
WHR has been found to be more efficient predictor of mortality than BMI or just waist circumference.
What is abdominal obesity?
Fatty tissues can get deposited in different locations in the body, like abdomen, gluteal regions, thighs, and beneath the skin. When the predominant deposition of fat is intra-abdominal, it is called abdominal or central obesity. Intra-abdominal and abdominal skin fat have much more significance as compared to the subcutaneous fat in the buttocks and lower extremities. This can be easily judged by determining the waist-to-hip circumference ratio. Some of the important complications of obesity like diabetes, and hypertension, are linked more strongly to intra-abdominal body fat than to overall obesity.
So why do we become obese?
Simple, when our energy intake is more than the energy expenditure. Body weight regulation is a complex interplay between different body systems that are influenced by energy intake and expenditure.
Central to all this, is a hormone called Leptin. Leptin is a hormone derived from adipocytes, or fat cells in our body, and acts in a certain area of our brain called Hypothalamus, to influence appetite, regulation of other metabolic hormones, and our energy expenditures.
So any factor that increases appetite or decreases energy expenditure or a combination of the two will result in a positive energy balance, and thereby will cause weight gain.
The body has certain mechanisms by which it can regulate energy expenditures as per the body weight. This means that your body will spend less energy in case you start fasting, and will spend more energy when your weight increases. This is where the concept of “set point” comes into picture, as the body is trying to maintain a particular weight over time by managing its energy balance. With weight loss appetite increases, and energy expenditure falls. Similarly with overfeeding appetite decreases and energy expenditure becomes more, however this balance by our body can fail and then lead to increase in body weight.
Do the obese really eat more?
Some obese individuals argue that they don’t eat anything, still they are obese. However, this has been now been scientifically disproved. As individuals gain more weight, their metabolically active lean tissue mass also increases, and this increases their average energy expenditure. This means, that just to support their more body weight, the obese individuals have to eat more as compared to lean individuals.
However, sometimes because of some underlying predisposition, individuals may become obese without having increased calorie consumption. But when they have gained weight, they need to keep taking more to sustain that weight.
In what all ways do we spend our energy?
It is also important to understand ways in which our body spends energy. The most important of our energy expenditure is Basal Metabolic Rate, or BMR. This is the energy spent to maintain our baseline body functions at rest in a neutral temperature environment. Roughly BMR is 1kcal/kg/hour. This energy expenditure contributes almost 70 % of our total energy spent, and therefore a large part of our energy expenditure is fixed, and is the minimum possible energy requirement.
Energy used up for processing or metabolising the food that we eat is another important energy expenditure. Our body spends roughly 10 % of the total energy consumed in processing and storing extra energy for the future. So this is a fixed energy expenditure and is proportional to the amount of calories consumed.
Non-exercise activity thermogenesis(NEAT) is a new concept that has been linked to obesity. This is the energy expenditure that accompanies physical activities other than exercise such as activities of daily living, spontaneous muscle contraction, maintaining posture, and fidgeting. This energy expenditure increases with weight gain and roughly accounts for two-thirds of energy spent by obese individuals. This also is relatively fixed energy expenditure.
Exercise contributes to 5-10 % of our energy spent depending on our level of activity. During vigorous activity, consumption of energy by muscle tissue can increase upto 50 times than normal basal rate. Therefore, exercise is the most important variable in the entire energy homeostasis, and it underlies the importance of exercise in our endeavour to loose weight.
What are the metabolic disorders and syndromes associated with obesity?
Hypothyroidism: Deficiency of thyroid hormones is one of the commonest implicated causes of obesity. But this is not entirely true. Most of the weight gain in hypothyroidism is because of myxoedema, which is a waxy consistency of skin and subcutaneous tissues and is not increase in adiposity, as defined in obesity.
Cushing’s syndrome: Patient’s with excess on steroids, whether endogenous or iatrogenic, have central obesity, hypertension, and glucose metabolism disturbances. A physician does keep the possibility of this disorder while working p patients with obesity. If suspected, this condition can be ruled out by measuring steroid hormones in the body.
Brain tumours: Certain brain tumours like craniopharyngioma, or hypothalamic dysfunction are another rare causes of obesity. The exact underlying mechanism for obesity in these conditions is poorly understood.
Pancreatic insulinoma: Pancreatic tumours producing excess of insulin, causes hypoglycaemia, and thereby provides a feedback to the body to store more energy by simulating a pseudo-energy deficiency state. This condition is also rare.
Genetic syndromes: Certain genetic syndromes like Laurence-Moon-Beidel syndrome, Prader Willi syndrome are associated with obesity.
Does obesity decrease life expectancy?
Yes it does.
Obesity can lead to roughly doubling up of the risk of mortality rate from all causes as compared to normal weight individuals. Moderately obese individual life span can get shortened by upto 5 years.
Cardio vascular causes of death are the most important causes leading to mortality in obese individuals.
How does obesity increase risk to life?
Abdominal obesity has been shown to be a risk factor for atherosclerosis. Obesity is also associated with increased blood pressure and glucose intolerance or Diabetes type 2.
Obese individuals also have a tendency for Sleep apnoea. Other lung problems associated with obesity includes decreased functional capacity, and poor respiratory reserve volumes.
Obesity also affects liver. It initially causes fatty liver disease, and later can rarely lead to cirrhosis or liver cancer.
Incidence of certain cancer also increases in obesity. In males obesity leads to increased rates of gastro-intestinal tract cancers, like liver, colon and pancreas. In females rate of ovarian, cervical, breast and gall bladder cancer is increased with obesity.
Disclaimer: This article is meant for general public awareness only and can not substitute expert medical advice.