Overview
Metabolic syndrome is one of the most common, albeit under recognized, health conditions in the United States. More than one-third of adults over the age of 20, and more than two-thirds of adults over the age of 60 have it, yet many have never heard the term.
Despite its name, metabolic syndrome is not a single disease. Instead, it is a collection of related health conditions that tend to occur together. These conditions include excess fat around the waist, elevated blood pressure, elevated blood sugar, high triglycerides, and low levels of HDL ("good cholesterol"). Individually, each of these conditions increases the risk of chronic disease. When they occur together, that risk becomes substantially greater.
The importance of metabolic syndrome is the dysfunction in the body's metabolism that develops gradually over many years. If left unaddressed, metabolic syndrome can increase the likelihood of developing type 2 diabetes, heart disease, fatty liver disease, chronic kidney disease, cancer, and even sudden life threatening events such as a heart attack or a stroke.
The encouraging news is that metabolic syndrome is often preventable and, in many cases, reversible. Unlike many chronic diseases, its underlying causes are strongly influenced by lifestyle factors such as nutrition, physical activity, sleep, body composition, and long-term habits. Even modest improvements in these areas can meaningfully reduce health risks.
In this article, I will explain what metabolic syndrome is, why and how it develops, why it is one of the most important health concerns, and what the scientific evidence suggests are the most effective ways to improve metabolic health.
What is Metabolic Syndrome?
As stated above, metabolic syndrome is not a single disease with a single cause. Metabolic syndrome is best understood as a collection of different metabolic disturbances that often occur together. Clinically, metabolic syndrome is diagnosed when at least 3 of the following 5 conditions are present: Elevated waist circumference, impaired fasting blood glucose, elevated blood pressure, high triglycerides, and low HDL (commonly called "good cholesterol"). Each of those particular health conditions can increase the risk of various chronic diseases, but when they occur together the risk is substantially higher, especially for cardiovascular disease and type 2 diabetes. The bad news is that these conditions often occur together because they share many of the same underlying biological mechanisms. The good news is that because these are so closely related, when one of the conditions improves, the others often improve as well.
The cluster of the particular health conditions that comprise metabolic syndrome are not random. Researchers have understood that individuals with one of these abnormalities are more likely to develop the others over time. Although scientists and physicians continue to study the precise mechanisms responsible for this relationship, insulin resistance, excess visceral fat, chronic low-grade inflammation, genetic predisposition, and lifestyle factors all appear to contribute to the development of metabolic syndrome.
Importantly, metabolic syndrome is not an "all-or-none" condition. Metabolic health exists along a continuum. A person with two risk factors does not suddenly become healthy because they fall short of the diagnostic threshold, nor does someone become dramatically less healthy simply by developing a third risk factor. Instead, the diagnosis provides a practical framework for identifying individuals whose overall risk has become high enough to warrant focused intervention.
The 5 Diagnostic Criteria
Increased Waist Circumference
Excess body fat is a major risk factor for metabolic disease, but the location of where the body fat is stored determines the metabolic impact. Fat that accumulates within the abdomen and the surrounding organs is known as visceral fat. Visceral fat has a much stronger association with insulin resistance, inflammation, and cardiovascular disease than fat stored beneath the skin.
For most adults in the United States, abdominal obesity is defined as a waist circumference of:
Men: 40 inches (102 cm) or greater
Women: 35 inches (88 cm) or greater
These cutoffs may differ for some ethnic populations because disease risk occurs at different levels of abdominal fat.
Although body mass index (BMI) is commonly used to classify body weight, waist circumference often provides additional information because it more directly reflects abdominal fat distribution.
Elevated Blood Pressure
Blood pressure is the force of blood pushing against the walls of the arteries. Persistently elevated blood pressure places additional strain on the heart and blood vessels and increases the risk of heart attack, stroke, kidney disease, and other complications. Elevated blood pressure is often called "the silent killer" because symptoms are generally subtle and often unnoticed.
This criterion is met if either of the following is present:
Systolic blood pressure: 130 mmHg or higher
Diastolic blood pressure: 85 mmHg or higher
Or currently taking medication to treat hypertension
Because blood pressure naturally fluctuates throughout the day, a diagnosis should not be based on a single elevated reading, but consistent elevated readings done under standardized conditions warrents concern.
Elevated Fasting Blood Glucose
Blood glucose is the body's primary source of energy, but it must be kept within a particular range.
When blood glucose is elevated in the fasted state, it often indicates that the body is becoming less responsive to insulin, a condition we call insulin resistance. Over time, this can progress to prediabetes and eventually type 2 diabetes if left unaddressed.
This criterion is met when:
Fasting blood glucose is 100 mg/dL (5.6 mmol/L) or higher
Or the individual is taking medication to lower blood glucose
Many people with elevated fasting glucose feel completely healthy and have no noticeable symptoms, making routine screening particularly important.
Elevated Triglycerides
Triglycerides are a type of fat (lipid) found in the bloodstream. After eating, the body converts some excess energy that is not immediately needed into triglycerides, which are transported through the blood and stored in fat tissue for later use. This is a normal and necessary part of human metabolism.
While triglycerides are a normal and necessary part of human metabolism, chronically elevated levels are associated with insulin resistance, fatty liver disease, and increased cardiovascular risk.
This criterion is met when:
Triglycerides are 150 mg/dL (1.7 mmol/L) or higher
Or medication is being used to treat elevated triglycerides
Triglyceride levels can fluctuate considerably depending on recent food intake, alcohol consumption, illness, and other factors, which is why measurements should be taken while fasting under standardized conditions.
Low HDL Cholesterol
High-density lipoprotein (HDL) is often referred to as "good cholesterol," although HDL is actually a group of particles involved in transporting cholesterol.
Lower HDL levels are commonly seen in people with insulin resistance and metabolic syndrome.
This criterion is met when HDL cholesterol is:
Less than 40 mg/dL in men
Less than 50 mg/dL in women
Or medication is being used to treat low HDL
Although raising HDL itself has not consistently been shown to reduce cardiovascular risk, low HDL remains an important marker of metabolic health.