Avocados Can Help to Treat Metabolic Syndrome, says review

A new review of studies looking at the health effects of avocados finds that there is “satisfactory clinical evidence” that the fruit can help to treat metabolic syndrome.
[A selection of avocados]
Researchers suggest that avocado may help to tackle metabolic syndrome.

Metabolic syndrome is defined as a cluster of risk factors that can raise the risk of other health conditions, such as type 2 diabetes, heart disease, and stroke.

Risk factors include abdominal obesity, low levels of high-density lipoprotein (HDL) cholesterol – or “good” cholesterol – high triglyceride levels, high blood pressure, and high fasting blood sugar.

The presence of at least three of these risk factors warrants a diagnosis of metabolic syndrome.

According to the American Heart Association, metabolic syndrome affects around 23 percent of adults in the United States.

Adopting a healthful diet is considered one of the best ways to prevent or treat metabolic syndrome. The new review – recently published in the journal Phytotherapy Research – suggests that avocados should form a part of this diet.

Avocados are a fruit from the avocado tree, or Persea Americana, which is native to Mexico and Central and South America.

A number of studies have documented the possible health benefits of avocado. A study reported by Medical News Today in 2014, for example, found that eating half an avocado with lunch may aid weight loss, while more recent research linked the fruit to reduced levels of low-density lipoprotein (LDL) cholesterol, known as “bad” cholesterol.

These benefits have been attributed to the bioactive components of avocados, which include carotenoids, fatty acids, minerals such as calcium, iron, and zinc, and vitamins A, B, C, and E.

For their review, co-author Hossein Hosseinzadeh, of Mashhad University of Medical Sciences in Iran, and colleagues set out to determine how these components might help to combat the risk factors of metabolic syndrome.

Avocado has the strongest effect on cholesterol levels

To reach their findings, the researchers analyzed the results of various in vivo, in vitro, and clinical studies that investigated the effects of avocado on metabolic health.

Hosseinzadeh and colleagues found that the fruit has the strongest impact on lipid levels – that is, levels of HDL cholesterol, LDL cholesterol, total cholesterol, and triglycerides.

As an example, the team points to one study of 67 adults, of whom 30 had a healthy lipid profile and 37 had mild hypercholesterolemia. After adhering to an avocado-enriched diet for 1 week, both groups showed significant reductions in total and LDL-cholesterol and triglyceride levels.

“The reported mechanism of this effect was regulating of the hydrolysis of certain lipoproteins and their selective uptake and metabolism by different tissues such as liver and pancreas,” explain the authors.

“Another possible mechanism could be related to the marked proliferation of the liver smooth endoplasmic reticulum which is known to be associated with induction of enzymes involved in lipid biosynthesis.”

An ‘herbal dietary supplement’ to help treat metabolic syndrome

The review also uncovered evidence that avocado is beneficial for weight loss. The researchers cite one study that found overweight or obese adults who ate one avocado every day for 6 weeks experienced significant decreases in body weight, body mass index (BMI), and the percentage of body fat.

Additionally, the team identified a number of studies associating avocado intake with reductions in blood pressure among patients with hypertension, and evidence suggests that the fruit might also help to reduce atherosclerosis – the narrowing or hardening of arteries caused by a buildup of plaque.

Notably, Hosseinzadeh and colleagues found that it is not just the flesh of the avocado that can benefit metabolic health – the peel, seed, and leaves of the fruit may also help.

One study published in 2014, for example, found that a daily dose of oil extracted from avocado leaves led to reductions in total and LDL cholesterol and blood pressure.

Overall, the researchers conclude that avocado may be effective for the treatment of risk factors associated with metabolic syndrome, though further research is warranted. They write:

“In this review article, satisfactory clinical evidence suggested that avocado can be used as herbal dietary supplements for treatment of different components of [metabolic syndrome].

Although, avocado like other herbal products is safe and generally better tolerated than synthetic medications, there is limited scientific evidence to evaluate different side effects because of contaminants, or interactions with drugs. Besides, further studies need to be accomplished on the metabolic effects of different parts of avocado for other possible mechanisms.”

Food as Medicine: Carrot (Daucus carota, Apiaceae)

History and Traditional Use

Range and Habitat

Ubiquitous at any supermarket, the common root vegetable carrot (Daucus carota, subsp. sativus) is a biennial plant that is an excellent source of vitamin A (one cup contains approximately 600% of the recommended daily value) and fiber.1 Indigenous to Europe as well as parts of Asia and northern Africa, carrots now are cultivated commonly in a wide range of environments as they can withstand frosts.2 The colorful varieties of carrots, as well as their hardiness, make them popular with home gardeners.

Phytochemicals and Constituents

Favored for their sweet flavor and versatility, carrots not only supply an impressive array of vitamins and minerals, but also contain carotenoids such as alpha- and beta-carotene, lycopene, and the flavonoid quercetin. Though the orange carrot is the most well known in modern times, carrots appear in a number of colors including white, yellow, red, and purple.3 In fact, purple was the prevailing color for carrots until about four hundred years ago, when popular theory claims that the unusual orange variety was cultivated in Holland as a sign of Dutch nationalism to honor William of Orange. The exact reason why the orange cultivar became the dominant variety is unknown, though genetic evidence suggests that orange carrots developed from yellow ones.4

The different colors of carrots reveal their various concentrations of phytochemicals.5 Carotenoids give yellow, orange, and red carrots their colors, while anthocyanins produce the deep purple variety. Orange carrots contain high quantities of beta-carotene. Yellow carrots contain low quantities of beta-carotene, but higher levels of lutein, which may protect from age-related macular degeneration and be beneficial for eyesight. Red carrots contain lycopene — a potent antioxidant with potential anti-cancer activity — in concentrations similar to that of tomatoes. Red carrots also contain moderate levels of alpha- and beta-carotene and lutein. Purple carrots contain high levels of anthocyanins, antioxidants that have anti-inflammatory and cardio-protective properties. The white variety has low levels of these phytochemicals but contains high levels of potassium.

Historical Uses

The record of the use of carrots in herbalism dates back to the 10th century, with mentions in the Old English Herbarium and the Leech Book of Bald indicating the use of the root as an emmenagogue as well as a treatment for smallpox and cough.6 Around the world, both root and seed have documented historical uses, typically to promote menstruation or as a diuretic. A different species, the wild American carrot (D. pulsillus), has an ethnobotanical history among many American native tribes as a remedy for colds, fevers, itching, and snake bites.7

Modern Research

Current research suggests that carrots may possess anti-cancer properties,8-10 as well as benefits for people with high blood pressure11 and cardiovascular disease.12 Beta-carotene is converted by the body into vitamin A and is a powerful antioxidant, protecting the body from free radicals and maintaining healthy skin and eyes.13

Consuming large amounts of beta-carotene, especially from carrots, can result in a harmless side effect called carotenemia, which temporarily yellows the skin.13 Infants, whose commercial foods often contain carrot puree as an added ingredient, are most likely to get carotenemia. The yellowing effect subsides as the body processes the excess beta-carotene.

Carrots can be enjoyed cooked or raw, as they retain their nutrients during the cooking process.14 Their sweetness adds to their versatility and supports their use in both sweet and savory dishes. A sweet-and-spicy pickle, for example, enhances the carrot’s natural flavor and a pleasing crunch.


Nutrient Profile

Macronutrient Profile: (Per 1 cup raw carrots)

52 calories
1.26 g protein
12 g carbohydrates
0.23 g fat

Secondary Metabolites: (Per 1 cup raw carrots)

Excellent source of:

Vitamin A: 34,317 IU (~686% DV)
Vitamin K: 16.1 mcg (20% DV)

Very good source of:

Vitamin C: 11.4 mg (18% DV)
Dietary Fiber: 3.7 g (14.6% DV)
Potassium: 394 mg (11.3% DV)

Good source of:

Vitamin B6: 0.2 mg (9% DV)
Manganese: 0.2 mg (8.5% DV)
Molybdenum: 6.1 mcg (8.1% DV)
Thiamin: 0.1 mg (8.0% DV)
Niacin: 1.1 mg (5.6% DV)
Phosphorus: 53.7 mg (5.4% DV)
Magnesium: 18.3 mg (4.6% DV)
Folate: 17.1 mcg (4.3% DV)

DV = Daily Value, as established by the US Food and Drug Administration, based on a 2,000-calorie diet.


Recipe: Spicy Pickled Carrots

Adapted from Alton Brown15

Ingredients:

  • 1 lb. baby carrots
  • 2 cloves of garlic, peeled and crushed
  • 1 cup of water
  • 1/2 cup of sugar
  • 1 1/2 cups apple cider vinegar
  • 1/2 teaspoon yellow mustard seeds
  • 1 1/2 teaspoons kosher salt
  • 1 teaspoon dried chili flakes
  • 2 dried red chilies

Directions:

  1. Place carrots and garlic in a 1-quart, spring-top glass jar.

  2. In a non-reactive

    sauce pan

    , bring the water, sugar, cider vinegar, mustard seeds, salt, and dried chili flakes to a boil, stirring to dissolve the sugar and salt. Boil for 4 minutes.

  3. Slowly pour the pickling liquid into the jar, covering the carrots and garlic completely. Submerge the

    chilies

    in the jar and cool before sealing.

  4. Refrigerate for two days (for a milder pickle) or a week (for a spicier pickle). These will get hotter the longer they are kept.

References

  1. Basic Report: 11124, Carrots, raw. US Department of Agriculture National Agricultural Library. Available here. Accessed November 19, 2014.
  2. Taxon: Daucus carota L. Germplasm Resources Information Network – (GRIN) [Online Database]. National Germplasm Resources Laboratory. Available here. Accessed November 19, 2014.
  3. History of the Carrot Part Three: From Medicine to Food – A.D. 200 to 1500. World Carrot Museum website. Available here. Accessed November 19, 2014.
  4. History of the Carrot Part Five: The Road to Domestication and the Colour Orange. World Carrot Museum website. Available here. Accessed November 19, 2014.
  5. Arscott SA, Tarnumihardjo SA. Carrots of many colors provide basic nutrition and bioavailable phytochemicals acting as a functional food. Comprehensive Reviews in Food Science and Food Safety. March 2010;9(2):223-239. Available here. Accessed December 3, 2014.
  6. What the Ancient Herbalists Said about Carrots. World Carrot Museum website. Available here. Accessed November 19, 2014.
  7. Moerman DE. Native American Ethnobotany. Portland, OR: Timber Press; 1998.
  8. Bhanot A, Sharma R, Noolvi M. Natural sources as potential anti-cancer agents: A review. International Journal of Phytomedicine [serial online]. April 2011;3(1):9-26.
  9. Aggarwal B, Shishodia S. Molecular targets of dietary agents for prevention and therapy of cancer. Biochemical Pharmacology [serial online]. May 14, 2006:1397, 1421.
  10. Rana Z, Malcolm R. C, Christine L. Le M. Bioactive Chemicals from Carrot (Daucus carota) Juice Extracts for the Treatment of Leukemia. Journal of Medicinal Food [serial online]. November 2011;14(11):1303-1312.
  11. Potter AS, Foroudi S, Stamatikos A, Patil BS, Deyhim F. Drinking carrot juice increases total antioxidant status and decreases lipid peroxidation in adults. Nutr J. September 24, 2011;10:96.
  12. Buijsse B, Feskens E, Kwape L, Kok F, Kromhout D. Both α- and β-Carotene, but Not Tocopherols and Vitamin C, Are Inversely Related to 15-Year Cardiovascular Mortality in Dutch Elderly Men. Journal of Nutrition [serial online]. February 2008;138(2):344-350.
  13. Vitamin Library: Beta-Carotene. Andrew Weil, MD website. Available here. Accessed November 19, 2014.
  14. Rock CL, Lovalvo JL, Emenhiser C, Ruffin MT, Flatt SW, Schwartz SJ. Bioavailability of beta-carotene is lower in raw than in processed carrots and spinach in women. J Nutr. 1998;128:913-916.
  15. Firecrackers. Food Network website. Available here. Accessed December 3, 2014.