Obesity

What is obesity?

The definition of obesity varies depending on what one reads, but in general, it is a chronic condition defined by an excess amount body fat. A certain amount of body fat is necessary for storing energy, heat insulation, shock absorption, and other functions. The normal amount of body fat (expressed as percentage of body fat) is between 25-30% in women and 18-23% in men. Women with over 30% body fat and men with over 25% body fat are considered obese.

What is the health risks associated with obesity?

Obesity is not just a cosmetic consideration; it is a dire health dilemma directly harmful to one's health. Obesity also increases the risk of developing a number of chronic diseases including:

• Insulin Resistance: Insulin resistance (IR) is the condition whereby the effectiveness of insulin in transporting glucose (sugar) into cells is diminished. Fat cells are more insulin resistant than muscle cells; therefore, one important cause of IR is obesity. The pancreas initially responds to IR by producing more insulin. As long as the pancreas can produce enough insulin to overcome this resistance, blood glucose levels remain normal. This IR state (characterized by normal blood glucose levels and high insulin levels) can last years. Once the pancreas can no longer keep up with producing high levels of insulin, blood glucose levels begin to rise, resulting in type 2 diabetes, thus IR is a pre-diabetes condition.
• Type 2 (adult-onset) diabetes: The risk of type 2 diabetes increases with the degree and duration of obesity. Type 2 diabetes is associated with central obesity; a person with central obesity has excess fat around his/her waist, so that the body is shaped like an apple.
• High blood pressure (hypertension): Hypertension is common among obese adults. A Norwegian study showed that weight gain tended to increase blood pressure in women more significantly than in men. The risk of developing high blood pressure is also higher in obese people who are apple shaped (central obesity) than in people who are pear shaped (fat distribution mainly in hips and thighs).
• High cholesterol (hypercholesterolemia)
• Stroke (cerebrovascular accident or CVA)
• Heart attack: The Nurses Health Study found that the risk of developing coronary artery disease increased 3 to 4 times in women who had a BMI greater than 29. A Finnish study showed that for every one kilogram (2.2 pounds) increase in body weight, the risk of death from coronary artery disease increased by one percent. In patients who have already had a heart attack, obesity is associated with an increased likelihood of a second heart attack.
• Congestive heart failure
• Gallstones
• Gout and gouty arthritis
• Osteoarthritis (degenerative arthritis) of the knees, hips, and the lower back
• Sleep apnea
• Pickwick Ian syndrome (obesity, red face, under ventilation, and drowsiness)

What Causes Obesity?

The balance between calorie intake and energy expenditure determines a person's weight. If a person eats more calories than he or she burns, the person gains weight (the body will store the excess energy as fat). If a person eats fewer calories than he or she burns, he or she will lose weight. Therefore the most common causes of obesity are overeating and physical inactivity. At present, we know that there are many factors that contribute to obesity, some of which have a genetic component:

• Genetics. A person is more likely to develop obesity if one or both parents are obese. Genetics also affect hormones involved in fat regulation. For example, one genetic cause of obesity is leptin deficiency. Leptin is a hormone produced in fat cells, and also in the placenta. Leptin controls weight by signaling the brain to eat less when body fat stores are too high. If, for some reason the body cannot produce enough leptin, or leptin cannot signal the brain to eat less, this control is lost, and obesity occurs.
• Overeating. Overeating leads to weight gain, especially if the diet is high in fat. Foods high in fat or sugar (e.g., fast food, fried food and sweets,) have high energy density (foods that have a lot of calories in small amount of food). Epidemiology studies have shown that diets high in fat contribute to weight gain.
• A diet high in simple carbohydrates. Carbohydrates increase blood glucose levels, which in turn stimulate insulin release by the pancreas, and insulin promotes the growth of fat tissue and can cause weight gain. Some scientists believe that simple carbohydrates (sugars, fructose, desserts, soft drinks, beer, wine, etc.) contribute to weight gain because they are more rapidly absorbed into the blood stream than complex carbohydrates (pasta, brown rice, grains, vegetables, raw fruits, etc.) and thus cause a more pronounced insulin release after meals than complex carbohydrates.
• Frequency of eating. Scientists have observed that people who eat small meals four or five times daily, have lower cholesterol levels and lower and/or more stable blood sugar levels than people who eat less frequently (two or three) large meals daily. One possible explanation is that small frequent meals produce stable insulin levels, whereas large meals cause large spikes of insulin after meals.
• Slow metabolism. Women have less muscle than men. Muscle burns more calories than other tissue (which includes fat). As a result, women have a slower metabolism than men, and hence, have a tendency to put on more weight than men, and weight loss is more difficult for women.
• Physical inactivity. Sedentary people burn fewer calories than people who are active. The National Health and Examination Survey (NHANES) showed that physical inactivity was strongly correlated with weight gain in both sexes.
• Medications. Medications associated with weight gain include certain antidepressants (medications used in treating depression), anti-convulsants (medications used in controlling seizures such as carbamazepine and valproate), diabetes medications (medications used in lowering blood sugar such as insulin, sulfonylurea and thiazolidinediones), certain hormones such as oral contraceptives and most corticosteroids such as Prednisone. Weight gain may also be seen with some high blood pressure medications and antihistamines.
• Psychological factors. For some people, emotions influence eating habits. Many people eat excessively in response to emotions such as boredom, sadness, stress or anger. While most overweight people have no more psychological disturbances than normal weight people, about 30 percent of the people who seek treatment for serious weight problems have difficulties with binge eating.
• Diseases such as hypothyroidism, insulin resistance, polycystic ovary syndrome and Cushing's syndrome are also contributors to obesity.

How is body fat measured?

Measuring a person's body fat percentage can be difficult; therefore, two widely used methods are weight-for-height tables and body mass index (BMI). While both measurements have their limitations, they are reasonable indicators that someone may have a weight problem. The calculations are easy, and no special equipment is required. The BMI uses a mathematical formula that accounts for both a person's weight and height. The BMI equals a person's weight in kilograms divided by height in meters squared (BMI=kg/m2).

The table below has already done the math and metric conversions. To use the table, find the appropriate height in the left-hand column. Move across the row to the given weight. The number at the top of the column is the BMI for that height and weight.

BMI(kg/m2)	19	20	21	22	23	24	25	26	27	28	29	30	35	40
Height(in.)	Weight (lb.)
58	91	96	100	105	110	115	119	124	129	134	138	143	167	191
59	94	99	104	109	114	119	124	128	133	138	143	148	173	198
60	97	102	107	112	118	123	128	133	138	143	148	153	179	204
61	100	106	111	116	122	127	132	137	143	148	153	158	185	211
62	104	109	115	120	126	131	136	142	147	153	158	164	191	218
63	107	113	118	124	130	135	141	146	152	158	163	169	197	225
64	110	116	122	128	134	140	145	151	157	163	169	174	204	232
65	114	120	126	132	138	144	150	156	162	168	174	180	210	240
66	118	124	130	136	142	148	155	161	167	173	179	186	216	247
67	121	127	134	140	146	153	159	166	172	178	185	191	223	255
68	125	131	138	144	151	158	164	171	177	184	190	197	230	262
69	128	135	142	149	155	162	169	176	182	189	196	203	236	270
70	132	139	146	153	160	167	174	181	188	195	202	207	243	278
71	136	143	150	157	165	172	179	186	193	200	208	215	250	286
72	140	147	154	162	169	177	184	191	199	206	213	221	258	294
73	144	151	159	166	174	182	189	197	204	212	219	227	265	302
74	148	155	163	171	179	186	194	202	210	218	225	233	272	311
75	152	160	168	176	184	192	200	208	216	224	232	240	279	319
76	156	164	172	180	189	197	205	213	221	230	238	246	287	328

Table Courtesy of the National Institutes of Health

Body weight in pounds according to height and body mass index.

Below is a table identifying the risk of associated disease according to BMI and waist size

BMI	Category	Waist less than or equal to 40 in. (men) or 35 in. (women)	Waist greater than 40 in. (men) or 35 in. (women)
18.5 or less	Underweight	N/A	N/A
18.5 - 24.9	Normal	N/A	N/A
25.0 - 29.9	Overweight	Increased Risk	High Risk
30.0 - 34.9	Obese	High Risk	Very High Risk
35.0 - 39.9	Obese	Very High Risk	Very High Risk
40 or greater	Extremely Obese	Extremely High Risk	Extremely High Risk

Table Courtesy of the National Institutes of Health