Dr Louise Johnson unpacks the different types of fat and details why visceral fat tissue increases cardiovascular risk.
Metabolic and cardiovascular diseases are increasing worldwide due to the rise in the obesity epidemic. The metabolic consequences of obesity vary by the distribution of the adipose (fat) tissue.
Obesity is defined by an excess of body fat. The most common measurements are waist circumference and BMI (body mass Index). This is calculated by weight per meter squared.
It’s important to realise that not all fats are bad. There are two types of fat:
- Brown fat is metabolically neutral. The distribution of brown fat is usually the gluteal-femoral fat (the buttock and thigh).
- White fat is metabolic-active, producing hormones. The distribution of this fat is intra-abdominal (tummy fat) and ectopic fat (found around the heart, kidney, liver and vascular structures).
In 1947, a French physician first described the phenomenon that obese patients with diabetes or signs of cardiovascular disease had a central distribution of body fat. These findings were viewed with scepticism, and it took more than 35 years before this observation was supported.
Measurement of obesity
There are several methods to evaluate obesity.
WHR (waist hip ratio)
This measurement looks at the proportion of the stored fat around the waist and hip. It’s calculated by dividing your waist measurement by your hip measurement since the hips are the widest part of the buttocks. (W/H)
Normal value for women should be below 0.85 or less. A value of more than 0.9 or higher is a high risk for cardiovascular disease.
Normal value for a male should be 0.95 or below. A value of 1.0 and higher is at high risk for cardiovascular disease.
The measurement of a waist is the middle area between the lower rib and the upper crest of the hip. Normal waist circumference should be below 80cm for a female and 94cm for a male.
BMI (body mass index)
This is the calculation of the length of a person times two. The weight is divided by this value (w/hx2). Normal BMI is 18-24.
A very effective manner to evaluate abdominal fat is via an MRI scan since all the ectopic fat areas can also be viewed. Unfortunately, this is very expensive.
The presence of abnormal measurements as described above is usually also associated with abnormal blood values. This is called the metabolic syndrome. It was also previously called syndrome X or insulin resistant syndrome. It constitutes the following abnormalities:
- Abdominal obesity;
- Increased triglycerides on a lipogram;
- Low HDL (good cholesterol);
- Small dense LDL increased (bad cholesterol);
- Insulin resistance;
- Glucose intolerance if not a diabetic yet;
- Endothelial dysfunction (abnormal blood vessel lining);
- Increased risk for thrombosis.
In recent large studies, such as the Framingham Heart Study and the Jackson Heart Study, convincing evidence was gathered using the above measurements to prove the association between visceral fat (fat stored deep inside the belly, wrapped around the organs, including the liver and intestines) and cardiovascular disease. This association is independent of the patient’s metabolic control.
Why is visceral fat unhealthy?
Visceral fat has more glucocorticoid (cortisone) receptors. This causes preferential fat deposits to the tummy area as well as ectopic areas. This also induces insulin resistance in the liver and skeletal muscles.
Ectopic fat deposition
An abnormal fat in the liver, around the heart, kidney, pancreas and blood vessels are called ectopic fat and is associated with visceral fat and the metabolic syndrome.
A recent study, by Britton and Fox, showed that ectopic fat can be divided in two groups:
Predominantly systemic effects of fat
- Visceral fat
- Liver fat
- Skeletal muscle fat deposits
Preferential local effects of fat
- Around blood vessels
Abnormal fat in the liver is called non-alcoholic fatty liver disease (NAFLD). This is increased in uncontrolled Type 2 diabetes and high cholesterol.
NAFLD can precede diabetes and cardiovascular disease. It can be diagnosed by an ultrasound that shows the fat content. It’s also increased in obesity.
Excessive fat in visceral obesity is deposited around the heart and in the heart muscle. This can cause heart problems, such as diastolic dysfunction (difficulty in filling the heart with blood) and heart failure.
What can be done about visceral or tummy fat?
- Adjust your diet by restricting calories.
- Exercise regularly, such as walking, cycling or swimming.
Nobody likes to talk about fat. It’s important to remember that not all fats are the same. Do the measurements discussed and a blood test fasting to check for triglycerides. This is the first step in not only preventing cardiovascular disease but also stroke and cognitive impairment in later years.
Get a good healthcare team on your side and start working.
MEET THE EXPERT
Dr Louise Johnson is a specialist physician passionate about diabetes and endocrinology. She enjoys helping people with diabetes live a full life with optimal quality. She is based in Pretoria in private practice.
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