Yes, fasting can raise cholesterol, and sometimes substantially. In healthy, non-obese people, prolonged fasting has been shown to increase LDL cholesterol by as much as 66% and total cholesterol by about 37%. The effect depends heavily on the type of fasting, how long it lasts, and your body composition. Here’s what’s actually happening inside your body and what it means for your health.
Why Fasting Pushes LDL Higher
When you stop eating, your insulin levels drop. That drop sets off a chain of events in your fat cells and liver that directly raises cholesterol in your blood. First, your fat cells start releasing stored fatty acids into your bloodstream to fuel your body. Your liver picks up those fatty acids and packages them into particles called VLDL, which eventually become LDL particles. So your liver is essentially producing more cholesterol-carrying particles because it’s processing more fat.
At the same time, your liver becomes worse at clearing LDL from the blood. Insulin normally helps maintain the receptors on liver cells that pull LDL out of circulation. When insulin drops during a fast, fewer of those receptors are active, so LDL lingers longer in the bloodstream. You’re getting a double hit: more LDL being made and less LDL being removed.
Growth hormone also rises during fasting, which accelerates the breakdown of fat stored in your cells. This further increases the flow of free fatty acids to the liver and compounds the effect on cholesterol levels.
How Much Cholesterol Rises During Extended Fasts
The magnitude of the increase depends on how long you go without food. A systematic review and meta-analysis of water-only fasting found that LDL rises progressively over the first 10 days or so, then begins to level off or partially reverse. Total cholesterol follows a similar pattern, with the biggest jumps occurring in fasts lasting more than three days and stabilizing around day five.
One study of healthy, non-obese subjects found particularly dramatic numbers. Total cholesterol jumped from about 189 mg/dL to 260 mg/dL, a 37% increase. LDL cholesterol nearly doubled, rising 66% from roughly 114 mg/dL to 189 mg/dL. Apolipoprotein B, a protein that tracks the actual number of harmful cholesterol particles in your blood, rose by 65% as well. That last number matters because ApoB is considered a more accurate marker of cardiovascular risk than LDL alone, and it climbed in lockstep with LDL during fasting.
HDL cholesterol, often called “good” cholesterol, moves in the opposite direction during longer fasts. It tends to drop after about three days and continues declining as the fast extends. Short fasts of 36 hours or less generally don’t affect HDL concentration much, though they may shift the size of HDL particles in ways researchers are still working to understand.
Intermittent Fasting Has a Different Profile
If you practice time-restricted eating (like 16:8 or one meal a day), the picture looks quite different from multi-day water fasts. An umbrella review of intermittent fasting research found that these shorter fasting windows have limited and inconsistent effects on LDL, HDL, and total cholesterol. The most reliable benefit is a modest reduction in triglycerides, particularly in people who are overweight.
This makes biological sense. During a 16- or 18-hour fast, your insulin drops enough to tap into fat stores for energy, but the duration isn’t long enough to drive the sustained, large-scale fat mobilization that floods the liver with fatty acids. You’re dipping into the fasting state rather than living in it, so the cholesterol effects stay relatively small.
That said, “inconsistent” doesn’t mean “zero.” Some individuals do see LDL changes with intermittent fasting, and those responses likely depend on genetics, body fat levels, and what they eat during their feeding windows.
Why Lean People May Be Hit Harder
There’s a recognized pattern called the lean mass hyper-responder phenotype, where people with low body fat experience a pronounced spike in LDL when they cut carbohydrates or fast. These individuals typically show very low triglycerides and high HDL alongside their elevated LDL, a combination that doesn’t fit the usual cardiovascular risk profiles.
The working explanation is that leaner people, with less subcutaneous fat to buffer the process, see increased VLDL secretion from the liver when energy needs shift toward fat metabolism. Their bodies are essentially moving more cholesterol through the bloodstream to deliver fuel because they have fewer fat reserves to draw from slowly. The exact cause isn’t fully established, and genetic factors likely play a role, but if you’re lean and fasting, you’re more likely to see a significant cholesterol increase than someone carrying more body fat.
What This Means for Your Blood Test
Standard cholesterol tests typically require 9 to 12 hours of fasting beforehand. This is a much shorter window than the multi-day fasts that produce dramatic LDL spikes, but it’s worth knowing that even this routine overnight fast is designed to give a baseline reading of your lipid levels without the influence of a recent meal. The fasting requirement primarily helps get an accurate triglyceride reading, since triglycerides fluctuate significantly after eating. Some newer guidelines allow non-fasting lipid panels, so follow whatever instructions your provider gives you.
If you’ve been doing a multi-day fast or an extended water fast and then get blood work done, your results will likely show elevated LDL and total cholesterol that don’t reflect your typical levels. This is a temporary, fasting-induced state, not necessarily your baseline cardiovascular risk profile. If you want an accurate picture of your usual cholesterol levels, get tested during a period of normal eating after fasting only the standard 9 to 12 hours overnight.
Are the Increases Dangerous?
This is the part researchers are still sorting out. The cholesterol increases during prolonged fasting appear to be temporary and largely reverse when normal eating resumes. The body is mobilizing stored energy, and cholesterol particles are the transport vehicles for that process. A short-term spike in LDL during a fast is metabolically different from chronically elevated LDL driven by genetics or a long-term dietary pattern.
However, “temporary” doesn’t automatically mean “harmless.” The 65% increase in ApoB seen during fasting in one study reflects a real increase in potentially harmful particles circulating through your arteries. Whether repeated cycles of fasting-induced cholesterol elevation cause cumulative damage to blood vessels is something that hasn’t been definitively answered. People with existing cardiovascular disease or familial hypercholesterolemia should be especially cautious about extended fasts, since they’re starting from a higher baseline and adding further LDL burden.
For intermittent fasting, the risk profile looks more favorable. The modest triglyceride reduction without major LDL increases suggests that shorter fasting protocols carry less lipid-related concern and may even offer a small benefit for people with elevated triglycerides.