Obesity in children – genetics, environments and more…

How is obesity defined in children?

We all realize that the number on the scale is not the only thing that defines whether a child is overweight. For example, if we hear of a child weighing 30kg, it does not really tell us much… if the child is 3 years old then 30kg is very high, and if they are 15 years old then that number is very low.

Obesity is actually better defined with the help of our BMI (Body Mass Index), a measurement that represents the proportion between the body weight and height, and this measurement can indicate whether our body is within the normal range. BMI is calculated using a simple formula as follows: weight in kilograms divided by the square of the height in meters.

A normal BMI in adults can be anything between 18 and 25. However, since children are not just tiny adults, for children even a BMI of 13 can be normal… The range of normal weights and heights varies with age, so does BMI.

This is why when we compare BMI in children, we do so by looking at percentiles (similarly to weight and height percentiles). These percentiles are made to match age and sex.

Note that we use BMI in children 2 years and older only.

How are overweight and obesity defined in children?

Overweight – a child with a BMI at or above the 85^th percentile for age and sex

Obese – a child with a BMI at or above the 95^th percentile for age and sex

Morbid obesity – a child with a BMI at or above 120% of the 95^th percentile for age and sex or a BMI of 35 and above

This simple BMI calculator, available on the CDC website may be useful and can help calculate your child’s BMI and corresponding percentile. Note that the CDC uses slightly different percentiles than the ones used by the World Health Organization (WHO).

How common is obesity in children?

According to data published by the World Health Organization and in the paper that I mentioned at the beginning of my post, the prevalence of obesity tripled between 1957 and 2016 with an increase seen in most of the countries around the world. It is therefore considered a pandemic, despite it being slower and more gradual than other pandemics we are familiar with…

Here are a few more interesting points:

• 39% of adults in the world are overweight, 13% are obese.
• In 2016, 340 million adults and children between the ages 5-19 years were either overweight or obese.
• In 2020, about 39 million children under the age of 5 years were either overweight or obese.

What causes obesity in children?

Obviously, there isn’t only one cause for obesity in children. The cause of obesity is multifactorial.

What does this mean? Multifactorial means a combination of many different factors, genetic and environmental, that may affect the balance that our body requires to keep the amount of energy we consume and utilise at an equilibrium. Obviously, there are genetic and familial tendencies behind different body figures, metabolic functions and so forth. At the same time, however, environmental factors, especially our lifestyles, have a significant impact on our body figures as well.

Technological advancement has many different advantages, but there is no doubt that it has its disadvantages too. One of its main disadvantages is that it has led to less healthy lifestyles…

We tend to exercise less, eat more processed foods, work in stressful environments and all of these can lead to an increase in weight. We also tend to pass on our habits to our children.

It is important to note that nutrition and exercise are not the only environmental factors that may affect obesity. Some of the environmental factors are not within our control. For example, gestational diabetes in a mother can lead to obesity, or even metabolic syndrome (a combination of obesity, diabetes and hypercholesterolemia), in their child when they reach adulthood.

There are other situations that can also cause obesity such as hormonal disorders (for example: Cushing’s Syndrome), a disorder in a specific area of the brain called the hypothalamus, certain medications and more.

In most cases, obesity develops around pre-K or kindergarten aged children or in adolescence. In the minority of cases, the cause of obesity presents in the first 2 years of life, and when that happens there is often a strong suspicion that the cause may be monogenic, that is, a condition caused by a mutation in a specific gene.

What is monogenic obesity?

Monogenic causes of obesity can be divided into 2:

1. Conditions that may be a part of a wider syndrome – these are syndromes that involve several other systems, such as Prader-Willi that may also lead to developmental delay. There are, of-course, many other syndromes as well.
2. Conditions that cause isolated obesity – these are caused by changes in the genes that are associated with the regulation of satiety. These conditions are characterised by normal birth weights, progressive increase in weight that presenting prior to the age of 2 years and a significant hyperphagia (increased appetite, a constant and often aggressive search for food after eating). Most of these conditions are inherited in a recessive manner, that means that both parents need to be carriers of the genetic change for the child to present with the clinical manifestation. Despite that, sometimes even if the child only inherits one abnormal gene, they may have an increased risk for obesity.

Due to the availability of advanced treatments, the topic of monogenic obesity is very “hot” in pediatric endocrinology. Nonetheless, as you’ve already read and seen, it is relevant only in children that have a more complex medical syndrome or in children younger than 2 years with significant hyperphagia.

Most children with obesity do not belong to either of these two categories.

What are the complications of obesity?

There are many different potential complications to obesity, some of them are short term and other are long term and these may increase the risk for heart and vascular diseases. Its important to note that most of these complications are reversible in childhood and improve with a reduction in weight and an improve in BMI. These are the main complications:

• Hypercholesterolemia, that means high cholesterols and/or triglycerides not within normal limits.
• Insulin resistance and diabetes type II
• Fatty liver – manifests in an increase in liver enzymes and a fatty appearance of the liver on ultrasound, which may affect the liver function.
• Obstructive sleep apnea – it is important to identify and treat this condition as it may lead to a reduction in quality of life, behavioural abnormalities, a decrease in learning capabilities, an increase in the risk for hypertension and more.
• Increased intracranial pressure – causes headaches and visual disturbances. This condition may seriously risk vision if it is not treated in time.
• Orthopedic manifestations – back pain, knee and thigh pain, scoliosis (read here), arthritis, slipped capital femoral epiphysis and more.
• Cosmetic manifestations including gynecomastia (breast enlargement) in adolescents.
• Effect on sexual development – in girls, obesity may lead to precocious puberty and in boys it may lead to late puberty.
• Polycystic ovaries in girls – menstrual irregularities, hirsutism, acne and fertility disorders in adulthood.
• Mental difficulties – a possible complication that should never be ignored and should always be treated.

How can obesity in children be prevented or treated?

In most cases, obesity can be prevented… it is therefore important to steer our children towards balanced and healthy diets and lifestyles, including physical exercise.

In cases where a child is suspected to be overweight or obese, it is important to consult with the primary care physician for a full history and physical examination, including body measurements and a BMI calculation. This is important in order to identify possible underlying medical causes and complications that can be treated. Following history taking and physical examination, the physician will decide whether further investigations need to be performed.

It is also important to address the mental state of the child as being overweight can have a huge effect on their mood, their social state and more.

The child will be referred to a dietician, physical exercise, psychological care, etc., as needed.

In terms of targets for ideal weights – children, in contrary to adults, are lucky… the goal is not always an absolute reduction in weight. In those that are still growing, sometimes the aim is mainly to just continue growing in height, without gaining weight, and this alone can bring about an improvement in BMI.

Beyond the change in habits, children in certain age groups are sometimes offered medication to help with diabetic and cholesterol complications.

In severe cases, there is also an option for bariatric surgery. These are usually performed in adolescents 18 years or older, but in certain cases they may even be performed in children as young as 13 years.

In summary, in the majority of the cases, weight is under our own control. It is important to remember that our children look up to us, and we should always try to be good role models for the sake of our children’s health and everyone’s health. Keep in mind that unfortunately we do not have magic solutions for being overweight and obese. Losing weight requires hard work, motivation, patience and lots of love and support.