What Is Metabolic Syndrome, and Can You Have It at a Normal Weight?
Metabolic syndrome is a pattern across five markers, not one number. What each marker reflects, and why it shows up at a normal weight too.
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What is metabolic syndrome? It is a name for five markers that tend to cluster together: a larger waist, raised triglycerides, low HDL (high-density lipoprotein) cholesterol, raised blood pressure, and raised fasting glucose. Under the harmonized definition that several major heart and diabetes organizations agreed on in 2009, you need only three of the five boxes checked to be diagnosed, and it doesn't matter which three. You can also have it at a normal weight, because no single marker, waist included, is required. In a US national survey that used a broader definition of its own, nearly one in four normal-weight adults had two or more cardiometabolic abnormalities, which is why a number on the scale can't rule the pattern out.
The five markers, and what each one reflects
Alberti and colleagues described metabolic syndrome as a cluster of risk factors for cardiovascular disease and type 2 diabetes that "occur together more often than by chance alone." Each of the five measures something different, and the cutoffs below come from their definition:
- Waist circumference. A larger waist is a simple stand-in for central obesity, which means extra fat stored deep in the abdomen. That fat sits near the liver and other organs, and it tracks more closely with insulin resistance than fat stored elsewhere on the body. The authors left the cutoffs to national or regional standards, since the right number varies by population. In the US, the line is about 40 inches (102 centimeters) for men and about 35 inches (88 centimeters) for women. European cutoffs run lower, at 37 inches (94 centimeters) for men and 31.5 inches (80 centimeters) for women.
- Triglycerides. Triglycerides are the main fat your blood carries, and your liver makes more of them when insulin resistance is present. The cutoff is 150 milligrams per deciliter (mg/dL) or higher, or taking medication for high triglycerides. High triglycerides are associated with a higher risk of heart disease, and they often appear alongside low HDL.
- HDL cholesterol. HDL is the so-called "good" cholesterol. The cutoff is below 40 mg/dL for men and below 50 mg/dL for women, or taking medication for it. Lower HDL is associated with a higher risk of cardiovascular events.
- Blood pressure. Blood pressure is the force of blood against your artery walls, measured with a cuff. The cutoff is 130 over 85 millimeters of mercury (mmHg) or higher, meaning either the top number (systolic) or the bottom number (diastolic), or taking blood pressure medication. Over years, high pressure strains the heart and damages artery walls.
- Fasting glucose. This is your blood sugar after a night without food. The cutoff is 100 mg/dL or higher, or taking medication for high blood sugar. A raised level is an early sign that your body is struggling to keep blood sugar in range, and it is associated with a higher risk of type 2 diabetes.
Two of the five usually don't show up on a lab report at all. Your waist and your blood pressure are measured in the room, so a lab printout on its own can't tell you whether you meet the criteria.
Why I read borderline numbers as a set
When I read a panel in clinic, I look at the direction of the numbers more than at which ones got flagged. I learn more from three or four numbers that each fall just inside or just outside their cutoff, all moving the same way, than from one number that came back flagged. Metabolic syndrome is built on that idea, since the diagnosis rests on the pattern across markers.
A German study gives an example of this in normal-weight adults. Eckel and colleagues worked with EPIC-Potsdam, a population-based study of adults in Potsdam, Germany, and compared those who went on to develop type 2 diabetes with those who didn't. The ones who developed diabetes had a larger waist, higher triglycerides, higher HbA1c (an estimate of average blood sugar over the past two to three months), and lower HDL cholesterol. The authors noted that these risk factors were higher, though "frequently still among the normal range." In other words, many of those numbers would have looked unremarkable read one at a time.
Can you have metabolic syndrome at a normal weight?
Yes. Wildman and colleagues analyzed 5,440 people in the US National Health and Nutrition Examination Survey (NHANES) from 1999 to 2004. Among normal-weight US adults aged 20 and older, 23.5 percent were metabolically abnormal. That is nearly one in four, or about 16.3 million adults in the United States. That study used its own definition: two or more of six abnormalities, including C-reactive protein (a marker of inflammation) and an insulin resistance score. It overlaps with the five standard criteria without matching them. In that group, older age, lower physical activity, and a larger waist were linked with the clustering.
A 2017 review by Stefan and colleagues put the share of normal-weight adults who are metabolically unhealthy at about 20 percent, roughly one in five. Compared with people of normal weight who are metabolically healthy, those people had more than three times the risk of dying from any cause, having a cardiovascular event, or both.
A 2013 meta-analysis by Kramer and colleagues pooled eight studies covering 61,386 people. Using metabolically healthy people of normal weight as the reference, all three metabolically unhealthy groups had a similarly elevated risk of death or cardiovascular events. For the normal-weight group, the relative risk was 3.14, a bit over three times the reference group's risk. For the overweight and obese groups, it was 2.70 and 2.65, or roughly 2.7 times the reference group's risk in both cases. Estimates vary from study to study. These are also averages across large groups, which means they can't predict what will happen to any one person.
Body mass index (BMI), a number calculated from height and weight, says little about any one person's metabolic health. Two people with the same BMI can have very different waist sizes, blood pressure readings, and lab results, and those are the measures the definition uses. If you'd like to go deeper on the blood sugar side, a normal A1c with high fasting insulin covers the test that shows your body making extra insulin to hold glucose steady. Separately, the post on where the evidence on improving insulin resistance is strongest explains the muscle side of the story.
Questions for whoever orders your labs
If your results show a few markers drifting the same way, you can ask the clinician who orders your labs to look at them as a set. A few questions that help:
- Have my waist and blood pressure been measured alongside this bloodwork?
- Do three or more of the five markers fall outside their cutoffs?
- Which of these numbers has moved since my last panel, and in which direction?
Some people also want to know how the gut fits in, and the post on the gut microbiome and blood sugar covers that. Everything else in this series is collected on the diabetes and metabolic health hub.
If you want a more structured approach to metabolic health, the Wayfinder's Well membership includes the full educational library, and Beyond Blood Sugar, an upcoming course on diabetes, will arrive in three parts.
FAQ
How many criteria do you need to have metabolic syndrome?
Under the harmonized definition agreed by several major heart and diabetes organizations in 2009, three abnormal findings out of five qualify. No single marker is required, so waist size doesn't have to be one of the three. The five are waist, triglycerides, HDL cholesterol, blood pressure, and fasting glucose.
Can thin people have metabolic syndrome?
Yes. The 2009 definition makes no single marker compulsory, so someone can meet three of the five without a large waist. Researchers studying normal-weight adults have found the same pattern, each team using its own definition. In a US national survey from 1999 to 2004, 23.5 percent of normal-weight adults, nearly one in four, had two or more of six cardiometabolic abnormalities. A 2017 review put the share of normal-weight adults who are metabolically unhealthy at about 20 percent, roughly one in five. A normal body mass index doesn't rule the pattern out.
Is metabolic syndrome the same as prediabetes?
No. Prediabetes is about blood sugar alone, while metabolic syndrome is a cluster of five markers that includes fasting glucose along with waist, triglycerides, HDL cholesterol, and blood pressure. The two often travel together, and someone can have one without the other.
Why does waist size count when weight doesn't?
The criteria measure where fat is stored rather than how much a person weighs. Extra fat around the abdomen is called central obesity. It is associated with more visceral fat (fat stored deep around the organs) and with metabolic dysfunction, even in people whose total body weight is in the normal range. The 2009 authors left waist cutoffs to national or regional standards for now, because the right number differs between populations.
What should I do if my labs show several borderline numbers?
It helps to bring the whole panel to whoever orders your labs and ask them to look at the markers together. You can also ask whether your waist and blood pressure have been measured alongside the bloodwork, since two of the five criteria usually don't show up on a lab report. Any decision about medication belongs with that clinician.
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