Doctors have traditionally ordered cholesterol tests to be drawn after an overnight fast. But this requirement causes a significant burden on both sides of the health care equation. Most people hate to fast. Skipping meals is particularly difficult for active people, people with diabetes, and children.

Yet coming back for another visit is even more of a hassle, so many people just don't bother. And it has been a drain for doctors, too, resulting in repeat test orders, phone calls, and patient visits. International guidelines published last month in the European Heart Journal became the latest official recommendation against routine fasting for cholesterol tests.

These guidelines defend what many health care systems and many doctors including me have been practicing for several years already. They should be met with universal acceptance, even if takes a while. There are several scientific reasons supporting this change. When doctors test for cholesterol, we almost always order a group of tests called a lipid panel lipids are fat-containing molecules.

This panel typically includes four separate measures:. Lipids have traditionally been drawn after a fast for two main reasons. The first was to minimize variation, since eating can affect some lipid levels. The second was to produce a better calculation of LDL-cholesterol, which is often derived from an equation thought to provide highly distorted results after eating.

However, more recent studies have largely negated these concerns. Scientists now agree that eating has only slight, clinically insignificant effects on three parts of the lipid profile: total cholesterol, and both HDL- and LDL-cholesterol.

Food does raise triglyceride levels for several hours, usually to a modest degree. After a high fat meal these increases can be striking. Therefore, a doctor may still order a fasting test of triglycerides if non-fasting values are significantly elevated.

Perhaps more important, large-scale analyses have shown that non-fasting lipids don't weaken the connection between cholesterol levels and harmful events like heart attack and stroke.

In fact, post-meal measures are thought to strengthen the ability of lipid levels to predict cardiovascular risk. This observation may stem from the fact that most people eat several meals plus snacks during the day. That means we spend most of our time in a "fed" state, not a fasting state.

So lipid levels after eating may best reflect our normal physiology. A growing body of research suggests that eating for lengthy periods in the day, ranging from 12—15 hours, may disrupt the circadian rhythm and increase the risk of chronic diseases including heart disease , cancer, and type 2 diabetes.

Thus, a major goal of fasting, specifically time-restricted eating, is to reduce the time spent eating in the day by extending the overnight fasting period. The study of the relationship between circadian rhythms and food timing is called chrono-nutrition. Many of the benefits of intermittent fasting are attributed to daily fasting periods of no less than 12 hours, although some research suggests that a minimum of 16 hours of fasting may be required.

Generally, during 12—36 hours of uninterrupted fasting, the liver glycogen stores become depleted, overall metabolic processes are altered, and positive health effects are observed. Findings across animal and human research show favorable changes in cholesterol levels.

Elevated total cholesterol, LDL cholesterol, and triglyceride levels are risk factors for heart disease. Intermittent fasting can improve blood sugar control by reducing insulin resistance , and increasing insulin sensitivity.

This results in lower fasting blood sugar and glycated hemoglobin — HbA1c — levels. In fact, experimental research in adult males with type 2 diabetes showed the potential for intermittent fasting as a therapeutic approach that may reduce the need for insulin therapy.

Changes in body weight and composition are among the most studied effects of intermittent fasting. Research also noted that this method could result in fat loss. Fasting in a pattern — an eating window of 10 hours and a daily fast of 14 hours — can act on the risk factors of metabolic syndrome, including by reducing waist circumference, body fat percentage, and visceral fat.

Intermittent fasting can thus ease metabolic syndrome , a set of risk factors that increase the risk of heart disease and type 2 diabetes. A review of 2, adult females indicated that reducing calorie intake in the evenings, and fasting for longer periods at night, may lower inflammation and the risk of breast cancer and other inflammatory conditions.

Observational research of 26, adult males over a year period suggested that r educing late-night eating through time-restricted eating may significantly reduce the risk of heart disease. Intermittent fasting may be safe for heart and metabolic health, but according to a review , it may induce negative side effects in some people, such as:.

Additionally, most of the research on intermittent fasting is based on animal research, with little long-term human research available. Furthermore, a review found that only six out of alleged health benefits of intermittent fasting were supported by moderate- to high-quality evidence, and most findings were based on low-quality research.

This means that more rigorous human research on the long-term health benefits of intermittent fasting is warranted. Some research suggests that the health outcomes of intermittent fasting are no greater than those observed in calorie restriction diets. However, research on intermittent fasting shows a greater adherence over longer periods compared to calorie restriction, and suggests that it may be a more sustainable approach.

The Mediterranean diet is a renowned dietary pattern based on the traditional eating patterns of the Mediterranean basin. A major benefit of the Mediterranean diet compared to intermittent fasting is that similar results can be achieved without the need for fasting.

Intermittent fasting describes a variety of eating patterns that alternate periods of fasting and eating with a consistent, recurring pattern over the course of a week. Time-restricted eating is the most popular form of intermittent fasting and uses the principles of chrono-nutrition to lengthen night-time fasting and potentially reduce chronic disease risk.

However, most of the research on intermittent fasting is based on animal studies and human research is sparse and often of low quality. Alternative non-fasting diets that produce similar results to intermittent fasting include calorie restriction and the Mediterranean diet.

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A Quiz for Teens Are You a Workaholic? How Well Do You Sleep? Health Conditions Discover Plan Connect. Should You Fast Before a Cholesterol Test? Medically reviewed by Gerhard Whitworth, R. Fasting Testing Preparing Reading results Takeaway A doctor may recommend fasting beginning in the evening before a cholesterol test, especially if you take statins.

Do you need to fast? How is cholesterol tested? How should I prepare for my cholesterol test? How to read your results. How we reviewed this article: Sources. Healthline has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations.

We avoid using tertiary references. You can learn more about how we ensure our content is accurate and current by reading our editorial policy. Mar 16, Written By Rena Goldman. Jan 14, Medically Reviewed By Gerhard Whitworth, RN.

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