Grapes, enjoyed for millennia, are more than just a tasty fruit. Rich in polyphenols, fiber, and water, they offer a range of potential health benefits. This article explores the science behind the grape diet, examining its purported advantages and potential drawbacks.
Historical and Modern Perspectives on Grape Consumption
A 2021 review highlights that people have been eating and using grapes for as many as 6,000 years. Throughout history, people have believed grapes contain healing properties. People produce around 75 million tons of grapes each year worldwide, around half of which goes into wine production.
The Allure of the Grape Diet: Detoxification and Weight Loss Claims
The grape diet, often promoted as a "detox" plan, typically involves consuming only or mostly grapes for a short period. Proponents suggest this can cleanse the body of toxins and promote rapid weight loss. The grape detox diet was first popularized by author Johanna Brandt in the 1920s. Brandt claimed that grapes helped cure her stomach cancer.
However, these claims are largely unsubstantiated. The American Cancer Society concluded that there’s no evidence that the grape detox diet “results in objective benefit in the treatment of cancer in human beings.” Your body is already designed to detoxify itself on its own, according to Mayo Clinic. The body has a natural detoxification system working constantly to flush out toxins ingested through the air you breathe or the food you eat. The kidneys and liver both play essential roles in converting toxins from substances like alcohol, drugs, and tobacco into waste products, and then flushing them out through urine, feces, and sweat, according to the AND.
While calorie restriction may lead to initial weight loss, such a restrictive diet is unlikely to lead to long-term weight loss, too. It can even have a counterproductive effect by slowing your metabolic rate, or the number of calories your body burns, according to Whitney Linsenmeyer, PhD, RD, a spokesperson for the AND and an assistant professor of nutrition and dietetics at Saint Louis University in St. Louis.
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Potential Health Benefits of Grapes: A Scientific Overview
Despite the lack of evidence supporting the grape detox diet, grapes themselves offer several potential health benefits when consumed as part of a balanced diet.
Cancer Prevention
Grapes contain polyphenols, which predominantly occur the skin and seeds of grapes. A 2022 paper suggests proanthocyanidins, a type of polyphenol, may protect against the following types of cancer: liver, bladder, prostate, and cervical.
Resveratrol, another polyphenol mainly found in red grape skins, can block all stages of cancer formation, according to a 2023 review. The Cancer Research is investigating effects of proanthocyanidin compounds from grape seeds and skins. Laboratory studies suggest that they, or compounds gut microbes produce from them, may influence expression of genes related to cancer development.
In a human study of five colon cancer patients, researchers studied the effects of consuming grapes on colon tissue. The subjects consumed whole grape powder every day for two weeks; samples of healthy and cancerous colon tissues were taken before and after consuming the grape diet. The results showed that subjects consuming the equivalent of 2 1/2 cups of grapes for two weeks showed a 47% reduction in the expression of certain target genes involved in the WNT-signaling pathway that are responsible for promoting tumor growth in the colon. In a second study, 30 healthy subjects were randomly assigned to one of three diets: consuming either 1/3, 2/3, or one pound of grapes each day for two weeks. Samples of colon tissue were taken before and after consuming the grape diets. The results showed that grape consumption at all three levels inhibited the expression of Wnt pathway target genes and markers of mucosal proliferation involved in cancer promotion. The researchers noted that the potential benefits of grape intake are most significant for high-risk older individuals and individuals whose diet is high in arginine intake; both of these groups have an increased incidence of colon cancer.
Cardiovascular Health
Research suggests the bioactive compounds in grapes can help to prevent and treat cardiovascular disease. A 2021 systematic review and meta-analysis concludes that supplementing grape seed extract into the diet may benefit people who are at risk of cardiovascular disease because it may lower heart rate and blood pressure levels.
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A small 2020 randomized control trial investigated the effects of grape seed extract on heart health in obese males. The results suggested that grape seed extract could significantly reduce cardiac output in obese males. Polyphenols in grapes, such as quercetin and resveratrol, contain antioxidant properties, which may help to protect against cardiovascular disease and risk factors. Grape seed oil also contains linoleic acid, which research suggests supports heart health in animal models.
Grapes contain potassium, which can contribute to heart health by helping with blood pressure management and counteracting the effects of sodium.
Blood Pressure Management
Increasing potassium intake may help people manage their blood pressure. The amount of potassium in grapes varies depending on the variety and form. Although some research suggests that grapes and grape products may have a blood pressure-lowering effect, more research is necessary to investigate the extent of this.
Digestive Health
Grapes contain water and fiber, which can help people stay hydrated, keep bowel movements regular, and reduce the risk of constipation. Research suggests that total fruit intake can influence the symptoms of functional constipation by affecting stool consistency, gut microbiota, and stool frequency.
Skin Health
A 2022 study on mice suggests grape antioxidants may benefit certain skin conditions, including atopic dermatitis. This may be because grape polyphenols have anti-inflammatory effects.
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In a human pilot study, subjects consuming grapes (equivalent to 2.25 cups per day) showed increased resistance to sunburn and a reduction in markers of UV damage at the cellular level. Subjects’ skin response to UV light was measured before and after consuming grapes by determining the Minimal Erythema Dose (MED). Grape consumption was protective; more UV exposure was required to cause sunburn following grape consumption, with MED increasing on average by 74.8%.
Diabetes and Eye Health
Research from 2022 suggests a higher intake of fresh fruit may have protective benefits against type 2 diabetes in people with normal glucose tolerance. A 2021 narrative review highlights research suggesting resveratrol may help to stop or slow the progression of diabetic retinopathy in animal models. Certain polyphenols in grape seed extract may also help to improve diabetic retinopathy severity.
A 2022 review suggests resveratrol contains anti-inflammatory and neuroprotective properties that can benefit eye tissues, potentially protecting against glaucoma, age-related macular degeneration, cataract, uveitis, eye tumors, dry eye disease, and myopia. In this study, for 3 months mice either consumed a 5%, 10% or 15% grape-enriched diet - designed to mimic one, two, or three servings of grapes per day in humans - or a diet with no grapes. Researchers identified a dose dependent protective response, where the 15% diet nearly abolished any sign of cataracts.
Other Potential Benefits
Other health conditions grapes may benefit include nonalcoholic fatty liver disease, obesity, liver injury, and Parkinson’s disease. In this study, researchers looked at gene expression in groups of mice that had been on either a standard diet, a high-fat diet, or a high-fat diet with grapes added and found within each group unique alterations of gene expression. Grape supplementation altered gene expression in a way that mapped more closely with the standard diet, suggesting the ability to mitigate the negative effects of a high-fat diet. A second, and similar study by the same research team, investigated the role of diminished estrogen influence at menopause and its association with oxidative stress and resulting cognitive decline, heightened anxiety, and hypertension. The control animals had increased blood pressure, anxiety-like behavior, and learning memory impairment. They exhibited increased oxidative stress in the brain, serum, and urine, and lower amounts of an antioxidant enzyme in the brain.
Risks and Considerations of the Grape Diet
Despite the potential benefits, the grape diet and excessive grape consumption can pose risks:
- Nutrient Deficiencies: Consuming only grapes can lead to deficiencies in essential nutrients like proteins and fats.
- Unsustainable Weight Loss: Weight loss from restrictive diets is often due to water and muscle loss, not fat.
- Metabolic Slowdown: Severe calorie restriction can slow down your metabolism.
- Potential for Disordered Eating: Fad diets can contribute to an unhealthy relationship with food.
- Blood Sugar Spikes: Grapes are high in natural sugars, which may cause blood sugar spikes, especially for individuals with insulin resistance or diabetes.
- Pesticide Exposure: Grapes are often high on the Environmental Working Group's "Dirty Dozen" list, indicating high pesticide residue. Buying organic grapes can reduce this risk.
- Medication Interactions: Grapes may interact with certain medications, such as beta-blockers and blood thinners.
- Kidney Problems: Consuming too much potassium can be harmful to people whose kidneys are not fully functional.
Incorporating Grapes into a Healthy Diet
The best way to enjoy grapes is as part of a balanced diet. Here are some tips:
- Choose fresh grapes that are tight to the touch and free of wrinkles.
- Store grapes in the refrigerator to prolong freshness.
- Wash grapes before eating.
- Add grapes to salads, fruit cocktails, or freeze them for a refreshing snack.