Obesity

Obesity is defined as a body mass index (BMI)*An index used to assess a person’s size and estimate whether they are overweight. and a waist circumference above the norm.
BMI is calculated by dividing body weight (in kilograms) by height (in meters) squared. A result between 18.5 and 25 is considered normal, and a result between 25 and 29.9 indicates the person is overweight. A person is considered to be obese if their BMI is 30 or above, and morbidly obese if their BMI is 40 or above.
BMI is an approximative tool however. Body composition and body fat distribution around the body can vary between individuals with the same BMI. For example, some athletes have a high BMI because muscle is heavier than fat.

Waist size is often used in addition to BMI. It is a very simple tool measured using a metric tape measure, and indicates obesity when the measurement is above 88 cm (34.6 inches) for women, apart from in pregnancy, and above 100 or 102 cm (40 inches) for men.
Weight alone is not therefore enough to determine whether or not someone is overweight.

In pragmatic terms, any excess weight is caused by an imbalance between the amount of calories consumed and energy expended. If you consume more calories than your body needs you will gain weight, as extra fat is stored by the body. Obesity occurs when this imbalance continues for a length of time.

Generally speaking, obesity is linked to several environmental, physiobiological, genetic, and epigenetic factors. Obesity therefore has a number of causes. There has long been a debate about the responsibility held by the individual and society, in particular the food industry. Increasing portion sizes, the sale of products that are particularly high in fat and/or sugar, and the abundance and constant availability of food in our industrialized societies combined with omnipresent marketing mean that the individual has to take control of their life while navigating a world of permanent temptation. Scientists call this “an obesogenic environment”. The democratization of the car and the rise of ever more sophisticated advertising for high-calorie foods have contributed to making the modern human a sedentary animal who does not eat a balanced diet. There is also a link between excess weight and the amount of time spent in front of a television or computer screen.

However, individual behavior and external factors do not explain everything. A genetic predisposition to put on weight does exist, although having these genes is not enough alone to explain obesity.
One current theory is that people who are better able to put down fat stores would have been favored by natural selection, precisely because they were armed to survive in the event of a famine. However, this advantage turns into a disadvantage in a period of plenty.

Insufficient physical activity and eating too much or eating foods that are too high in calories are the main risk factors for obesity.

A family history of obesity can also play a role. We know that overweight children are more likely to become obese in adulthood if their parents are obese. Some modifications to gene expression without DNA mutation, referred to as epigenetic changes, seem to be the cause. In addition, several genes contribute to the production of leptin*A hormone sometimes referred to as the satiety hormone that regulates the body’s fat stores and the feeling of fullness., a hormone that affects appetite regulation and energy expenditure.

Body clock dysregulation (jet lag, irregular or insufficient sleep, eating at irregular times, etc.) can also put you at risk of excess weight gain and obesity because it affects appetite regulation and metabolism. An unhealthy diet can also feed back into the body clock and impair its function by means of the digestive hormones. Gut flora (microbiota) also seems to play an important role in obesity.

Finally, repeated dieting and/or dieting without medical supervision are often counterproductive, leading to a rapid regaining of the weight lost after a certain period of time (the yo-yo effect).

Medical care for obesity needs to be personalized to the patient and multi-disciplinary. It involves following a tailored exercise plan, eating a balanced diet, and, if necessary, taking medication. Surgery for obesity (bariatric surgery) is reserved for the most severe forms of the disease.

There are several types of surgery available in cases of severe obesity:

• A gastric bypass*A surgical technique that involves creating a gastric pouch for food that is separate to the rest of the stomach. This pouch is then linked directly to the intestine, which disrupts digestion and food absorption., often considered the gold standard procedure, creates a gastric “short-circuit” by linking the stomach to part of the small intestine located further along the digestive system.
• A gastric band*A surgical technique that consists of placing a band around the top of the stomach. When food is ingested, this small pouch fills up quickly, which causes a feeling of fullness. slows down the transit of food in the stomach and therefore limits the amount of food the patient can eat.
• A gastrectomy*A surgical technique that consists of removing two thirds of the stomach and in particular the external part that contains the ghrelin-secreting cells (the hormone that stimulates the appetite). involves removing part of the stomach to reduce not just the amount of food that can be eaten but also the secretion of ghrelin*A digestion hormone that stimulates the appetite. Ghrelin levels increase before a meal and reduce when the stomach fills up., a hormone linked to the feeling of hunger.
• Biliopancreatic diversion*A surgical technique that firstly consists of reducing the size of the stomach and then modifying the gastrointestinal tract to create two pathways. Food transits through the first, and the second is for gastric juices. The two then meet again in the small intestine. also entails removing part of the stomach. The aim is to stop the body absorbing nutrients well.

Obesity can contribute to a number of health problems including cardiac, joint, and respiratory issues. The main complications are type II diabetes*A chronic disease that affects the way the body regulates blood sugar (glucose) levels. It used to be known as adult-onset diabetes., cardiovascular diseases*A group of diseases affecting the heart and blood vessels., hypertension*A disease in which the blood pressure in the arteries is too high. and abnormally high concentrations of lipids in the blood (dyslipidemia*The abnormal accumulation of cholesterol or fatty acids (lipids) in the blood.). This is why obesity is considered to be an expression of the metabolic system, which is characterized by a set of physiological factors including:

• high blood pressure,
• too much sugar in the blood  (hyperglycemia*Abnormally high levels of glucose in the blood.),
• excess body fat around the waist,
• abnormally high cholesterol.

Possible complications associated with obesity also include:

• heart failure,
• sleep apnea,
• joint diseases (and osteoarthritis of the knee in particular),
• and, finally, depression.

We know that the risk of complications is higher if a person’s body fat is concentrated mainly around their stomach and hips. A more even body fat distribution (referred to as gynoid obesity*Gynoid obesity refers to when a person’s excess body fat mainly accumulates on the lower part of their body. Inversely, android obesity is when fat stores are located over the stomach. This is also called abdominal obesity.) is less likely to lead to other diseases.
People who are obese have a worse quality of life overall and a shorter life expectancy than people who are a normal weight. People who are simply overweight have a lower risk of developing diseases, however excess weight can worsen existing problems.

Any reduction in weight is important. Weight loss of 5–10% is enough to notably improve quality of life for an obese person as it reduces blood pressure and their risk of developing type II diabetes. Although it is never too late to start, it is best not to wait. It is generally harder to combat obesity if it started early in life.

When it comes to preventing obesity, the golden rules are to move as often as possible, eat reasonably sized portions of healthy food, and drink lots of water. Personalized dietetic support can be beneficial. At least 150 minutes of moderate physical activity should ideally be done each week (or 75 minutes of intense physical activity).

People with obesity should try to find a doctor they trust to carry out a full health assessment and plan professional care for them.

Obesity needs both a comprehensive and personalized approach starting with an exhaustive medical assessment. Support should be provided on a long-term basis. It may include conservative care such as:

• advice and dietetic and nutritional support,
• an assessment of physical capacity and rehabilitation to get back into physical activity,
• psychological support (for example in the form of cognitive behavior therapy, psychotherapy, mindfulness, or meetings with groups of patients who have undergone surgery),
• acupuncture or medical hypnotherapy.

Surgical procedures for obesity or bariatric surgery (for example a gastric bypass or a sleeve gastrectomy) are reserved for severe forms of obesity accompanied by complications (comorbidities). They include:

• an assessment of the contraindications for bariatric surgery,
• medical, psychological, nutritional, and behavioral preparation before the procedure,
• long-term follow-up.