(Editor’s note: This article is reprinted from The Nutrition Source newsletter of the Harvard T.H. Chan School of Public Health. The contents are for educational purposes and are not intended to offer personal medical advice. The Nutrition Source does not recommend or endorse any products.)
Does eating an apple every day really keep the doctor away? Apples are certainly popular—ranking among the top three fruits produced around the world. They are easy to store and transport, and as a result, are typically available year-round in the U.S. In this piece we’ll explore how apples may benefit health and the best types for baking versus munching straight off the core.
- Fiber, insoluble and soluble
- Phytochemicals (quercetin, catechin, chlorogenic acid, anthocyanin)
- Vitamin C
One serving, or one medium apple, provides about 95 calories, 0 gram fat, 1 gram protein, 25 grams carbohydrate, 19 grams sugar (naturally occurring), and 3 grams fiber.
Apples and Health
Apples are rich in quercetin and pectin, both of which are credited for supplying apples with their health benefits.  Quercetin is a flavonoid, a type of naturally occurring plant chemical that has antioxidant and anti-inflammatory effects. Pectin is a type of soluble fiber that may help prevent constipation and have a modest effect on lowering LDL, the “bad” cholesterol. Pectin is also fermented by beneficial bacteria in the colon, which produces short chain fatty acids that may play a role in the prevention of chronic diseases, including certain cancers and bowel disorders. [2,3]
Fresh, whole apples offer the most nutrients. Discarding the skin removes much of the fiber and the majority of flavonoids. Dehydrating or drying the apples removes vitamin C, which is predominantly in the flesh. In addition, sugar (along with extra calories) is often added to dried apples. Clear apple juice undergoes filtering and pasteurization, which removes most of the flavonoids and fibers. 
Overall research shows a benefit when adding apples to the diet. The studies below looked at the health effects of apples in the diet over time, or examined the effects of specific phytochemicals in apples.
- Cardiovascular health. Animal studies have shown that plant chemicals, particularly in the apple peel, combined with pectin fiber can help to protect against free radical damage in the heart and blood vessels and have cholesterol-lowering effects. [3,4] Human intervention studies using fresh apples, apple cider, or apple supplements show mixed results, showing no effect or other times lowering cholesterol.  A review of five clinical trials noted the effects of fruits on cardiovascular diseases, and found an improvement in cardiovascular parameters (decreased triglycerides and LDL cholesterol) with intakes of whole fresh apples or dried apples, though not with apple juice. 
- Population studies on coronary heart disease and flavonoid intake, including quercetin from apples, also show mixed results:
- A study of more than 66,000 women from the Nurses’ Health Study found that, when comparing the highest and lowest intakes of flavonoids, there was no difference in rates of heart attack or deaths from heart disease. 
- A cohort study following almost 75,000 Swedish men and women for 10 years found a significant association: lower risk of stroke was seen in the group with the highest intakes of apples compared with the lowest intakes. 
- Type 2 diabetes. The antioxidant effect of flavonoids in apples may protect cells from damage in the pancreas, an organ responsible for secreting insulin in response to extra sugar in the blood. An epidemiological study of more than 38,000 women in the Women’s Health Study followed for almost nine years supported a beneficial relation between apple intake and risk of type 2 diabetes. Those who ate one or more apples a day had a 28% lower risk of type 2 diabetes compared with those who ate none. Although the study established a link with apples in the diet, it did not show an association when examining specific flavonoids like quercetin. 
- Weight control. The fibers in apples can slow digestion, helping one to feel greater satisfaction after eating. After following three large prospective cohorts of 133,468 men and women for 24 years, researchers found that higher intakes of fiber-rich fruits with a low glycemic load, particularly apples and pears, were associated with the least amount of weight gain over time. Eating low glycemic load foods tends to produce fewer and smaller spikes in blood sugar, which may lessen hunger later on and prevent overeating. 
- Cancer: The phytochemicals and fiber in apples have antioxidant effects that may protect a cell’s DNA from oxidative damage, which is a precursor to cancer. Animal and cell studies have found that these chemicals can prevent new cancer cells from growing and the spread of existing cancer cells. Results from human studies are mixed, depending on the type of study performed.
- Specific cancers: Evidence suggests that a decreased risk of lung cancer with higher intakes of all fruits (including apples) applies mainly to smokers and former smokers. [9,10] In a meta-analysis of 41 case-control and cohort studies found that when comparing the highest with lowest levels of apple intake, there was a lower risk of lung cancer in both types of studies. It also found a lower risk of colorectal, breast, and digestive tract cancers in the case-control studies but not cohort studies.  Other epidemiological studies have shown a small association of higher intakes of fruit and a lower risk of colon and upper digestive tract cancers (e.g., esophageal, mouth, larynx).