Obesity is a chronic condition arising due to an excess amount of body fat. It is global issue that is becoming more and more prevalent. WHO suggests that approximately 13% of adults worldwide are obese. Obesity is less prevalent in many African and Southeast Asian countries and is highest in Europe and the Americas. In England, 26% of adults were classified as obese.
🔍 How do we calculate if someone is obese?
There are many ways to diagnose obesity, but the most common way is to use their Body Mass Index (BMI). It is a reasonable measure in the majority of people, but has drawbacks in pregnant women or people with a large amount of muscle mass. It does not account for sex, age, bone structure and other factors relevant to calculate the relative amount of body fat. Nevertheless, it is the standard test to determine obesity.
We can also use waist circumference measured just above the iliac crests, but this is less common.
The formula for BMI is:
Pathophysiology
It is naive to believe that caloric intake being greater than caloric expenditure is the only cause for obesity. Ultimately this is the reductionist cause of obesity. There are certain factors that can influence this imbalance, however:
- Genetic predisposition - there is no single gene that contributes to obesity but it is believed that multiple gene mutations, epigenetic factors and non-coding RNA that is involved.
- Behavioural dynamics - sedentary lifestyle, poor dietary habits, eating disorders, mental illness.
- Hormonal disturbances - hypothyroidism, hypercortisolism, insulinoma.
- Cultural influences - cultural practices, beliefs about beauty and body imagine, cuisines and eating habits etc.
- Environmental circumstances - low SES, adverse nutrition in-utero, micro biome.
- Medications - such as mirtazapine or steroids
It is important that we discuss appetite and energy homeostasis:
The hypothalamus processes hormones from the bloodstream, receives peripheral neural input, central cerebral input and also outputs signals to the arcuate nucleus to regulate appetite.
There are 2 populations of neurones in the arcuate nucleus that have opposing effects on appetite.
Let’s discuss 2 hormones that are important to affect the appetite inhibiting and stimulating neurones:
- Leptin - secreted by adipose tissue when fat is stored. It has negative feedback on the hypothalamus to inhibit appetite and indicate satiety.
- Ghrelin - secreted by the stomach primarily. It acts on the hypothalamus and the vagus nerve to increase appetite.
Obese individuals are in a state of leptin resistance and do not respond to increased leptin levels adequately.
We do not have a complete understanding of the peripheral pathways influencing appetite and energy homeostasis, and we have even poorer understanding of the higher cortical inputs (such as learned behaviours, likes, dislikes etc.) may affect food intake.
🔢 Classification
Let’s discuss BMI ranges and then we will look at the 5 classes of obesity.
Underweight - BMI <18.5kg/m²
Normal - BMI 18.5-24.9kg/m²
Overweight - BMI 25-29.9kg/m²
Obese - BMI >30.0kg/m²
- Class I - 30 - 34.9kg/m²
- Class II - 35-39.9kg/m²
- Class III - >40kg/m²
- Class IV - >50kg/m²
- Class V - >60kg/m²
⚠️ Risk factors
- Hypothyroidism
- Hypercortisolism
- Corticosteroid therapy
- >40 years
- Postmenopause
- Lower SES
- Sedentary lifestyle
- Alcoholism
- Poor diet
- Antipsychotic therapy
🧰 Management
- 🥇 Dietary changes - a 500-1000kcal/day deficit. Unbalanced and restrictive diets long term are not recommended.
- 🥇 Physical activity - evidence indicates weight loss is greater with diet + exercise than solely diet alone.
Psychological therapy and pharmacotherapy can be considered if there are co-morbidities such as diabetes, hypertension or dyslipidaemia.
Pharmacotherapy includes:
- Semaglutide - 0.25mg SC once weekly for 4 weeks. Cannot be prescribed in primary care.
- Orlistat - 120mg 3x daily taken just before or at the time of the meal. It can be prescribed in primary care. If they do not have 5% weight loss after in the first 3 months of using the drug, they should stop using it and other options should be considered.
Patients with a BMI >40 may be candidates for early bariatric procedures. This is particularly true for patients who have other conditions relating to their obesity such as hypertension and T2DM.
Let’s discuss some bariatric procedures:
- Restrictive operations
- Laparoscopic-adjustable gastric banding (LAGB) - normally 1st line but produces less weight loss, however, it has fewer complications.
- Sleeve gastrectomy - reduces stomach to about 15% of its original size.
- Intragastric balloon - ballon that takes up space in stomach. Can be left in for 6 months.
- Malabsorptive operations
- Biliopancreatic diversion with duodenal switch - reserved for class V obese patients.
- Mixed operations
- Roux-en-Y gastric bypass - both restrictive and malabsorptive.
Surgery can be considered in class III obesity if co-morbidities are present.
[PLEASE REVIEW BASED ON NG189]
Obesity in children is harder to diagnose as BMI varies with age. NICE recommends using UK 1990 BMI charts to give age and gender-specific data.
A BMI in above the 91st percintile is deemed overweight. A BMI above the 98th percentile is defined as obesity.
⚠️ Risk factors
- Lifestyle factors
- Asian children - 4x more likely than Caucasian children.
- Female children
- Taller children
Some conditions that can cause obesity in children are:
- Growth hormone deficiency
- Hypothyroidism
- Down’s syndrome
- Cushing’s syndrome
- Prader-Willi syndrome
🚨 Complications
Obesity in children can cause a multitude of issues:
- Orthopaedic issues
- Slipped upper femoral epiphyses
- Blount’s disease - abnormality of the tibia → bowing of legs
- MSK pains
- Psychological consequences - poor self-esteem, bullying.
- Sleep apnoea
- Benign intracranial hypertension
- Increased risk of
- T2DM
- Hypertension
- IHD
🧰 Management
NICE does not recommend dietary measures alone but instead it recommends a combination
🥇 Lifestyle modification is the mainstay of treatment for all ages and percentiles of BMI.
If the child is suffering psychosocial comorbidities as a result of their obesity (such as bullying, low self-esteem, anxiety, depression), then these can be managed too.
If the child is 12-18 years old we can consider pharmacotherapy:
- Orlistat - 120mg 3x daily.
- Liraglutide - 0.6mg SC once daily for 1 week. Cannot be prescribed in primary care.