Several factors lower HDL cholesterol, ranging from everyday habits like smoking and inactivity to deeper metabolic issues like insulin resistance and chronic inflammation. HDL below 40 mg/dL in men or 50 mg/dL in women is clinically considered low, and understanding what drives it down is the first step toward changing it.
Trans Fats Have the Strongest Dietary Effect
Trans fats are uniquely harmful to HDL. In a controlled trial published in the New England Journal of Medicine, swapping healthy fats for trans fats lowered HDL by an average of 7 mg/dL. That’s a meaningful drop, especially if your levels are already borderline. What makes trans fats worse than saturated fat is this double hit: they raise LDL (the harmful type) while simultaneously pulling HDL down. Saturated fat, by comparison, raised LDL in the same study but left HDL unchanged.
Trans fats still show up in some fried foods, packaged baked goods, and certain margarines, though food manufacturers have reduced their use significantly in recent years. Checking labels for “partially hydrogenated oils” is the most reliable way to spot them.
Sugar and Refined Carbs Suppress HDL
Diets high in added sugar and refined carbohydrates consistently push HDL levels down. Research in Cardiovascular Diabetology found that higher total sugar intake was associated with a 3.4% relative decrease in HDL, while diets with a high glycemic load (lots of quickly absorbed carbs like white bread, sugary drinks, and processed snacks) were linked to a 4.1% drop. These percentages translate to a few milligrams per deciliter, which adds up over time, especially alongside other risk factors.
The mechanism involves triglycerides. When you eat a lot of fast-digesting carbs, the liver produces more triglyceride-rich particles. Those particles essentially trade their triglycerides for cholesterol from HDL particles, making HDL smaller and easier for the kidneys to filter out. This same process plays out more aggressively in insulin resistance, which is covered below.
Insulin Resistance and Excess Weight
Carrying excess body fat, particularly around the midsection, is one of the most common drivers of low HDL. Studies consistently show a negative relationship between BMI and HDL levels. In one large analysis, morbidly obese individuals had average HDL levels roughly 25% lower than those at a normal weight. The relationship is dose-dependent: the higher the BMI category, the lower the HDL.
The underlying reason is insulin resistance. When fat cells become less responsive to insulin, they release more fatty acids into the bloodstream. The liver repackages these fatty acids into triglyceride-heavy particles. As triglyceride levels rise, a shuttle protein in the blood starts swapping triglycerides into HDL particles, replacing their cholesterol cargo. These triglyceride-loaded HDL particles then get broken down by enzymes and become small enough to be filtered out through the kidneys. The net result: fewer HDL particles circulating in your blood, and the ones that remain are less effective at their primary job of pulling excess cholesterol out of artery walls.
This is why low HDL rarely travels alone. It typically comes paired with high triglycerides, elevated blood sugar, and abdominal obesity, a cluster sometimes called metabolic syndrome.
Sedentary Lifestyle
Physical inactivity measurably lowers HDL. In a large population study from Luxembourg, people who were completely sedentary had an average HDL of 57.1 mg/dL, compared to 63.5 mg/dL in those who were moderately active. That 6-point gap is clinically significant, roughly the same size as the effect of smoking.
You don’t need extreme exercise to see a benefit. The biggest jump in HDL appeared between the sedentary group and those doing even a small amount of daily activity. People getting 30 to 60 minutes of vigorous activity per day had the highest HDL levels, averaging 64.5 mg/dL compared to 60.8 mg/dL in less active groups. Aerobic exercise appears to work by improving how the body processes triglycerides, which reduces the triglyceride-for-cholesterol swap that shrinks HDL particles.
Smoking
Cigarette smoking lowers HDL by about 4 mg/dL in men and 6 mg/dL in women, based on data from the Framingham Heart Study. That effect is persistent as long as you keep smoking but largely reversible. Former smokers showed no HDL deficit compared to people who never smoked, as long as they had been smoke-free for at least a year. Switching to cigars or pipes, however, didn’t restore HDL levels.
Chronic Inflammation
When the body is in a prolonged inflammatory state, whether from autoimmune conditions, obesity, chronic infections, or other causes, HDL takes a hit in both quantity and quality. During inflammation, the body floods HDL particles with a protein called serum amyloid A, which can increase by 500 to 1,000 times its normal level during acute flares. This remodeling shrinks the HDL pool and, more importantly, impairs HDL’s ability to pull cholesterol from artery walls.
Research on people with systemic lupus erythematosus found that their HDL had significantly reduced cholesterol-clearing ability and had lost its anti-inflammatory properties. In animal studies, both infection-driven and sterile inflammation caused HDL levels to drop while triglycerides rose. Chronic, low-grade inflammation (the kind associated with obesity or poorly controlled autoimmune disease) may not cause the dramatic HDL crashes seen in acute illness, but it steadily erodes HDL function over time.
Genetic Causes
Some people have persistently low HDL despite a healthy lifestyle, which can point to an inherited condition. Familial HDL deficiency is a genetic disorder that keeps HDL levels well below normal and raises the risk of cardiovascular disease before age 50. A more severe form, Tangier disease, drives HDL to near-zero levels and comes with distinctive signs like enlarged, orange-colored tonsils, nerve problems, and cloudy corneas.
These conditions are rare, but they matter if your HDL stays stubbornly low despite addressing all the modifiable factors above. A lipid specialist can test for genetic variants that affect HDL production or clearance.
How These Factors Overlap
In practice, low HDL is rarely caused by a single factor. Someone who is overweight, sedentary, and eating a diet high in refined carbs is getting hit from three directions at once, all converging on the same triglyceride-driven pathway that shrinks and destroys HDL particles. This is actually useful to know, because it means addressing even one or two factors (losing some weight, adding regular activity, cutting back on sugar) can produce a compounding benefit rather than a small isolated change. The most reliable way to raise HDL is to reverse the things suppressing it, and in most cases, those factors are modifiable.