What Can Something as Simple as the Skin of Fruit Tell Us About Nutrition?

Raspberries

Caveman Doctor was recently asked if he peels the skin off of fruit when he eats it, as well as his thoughts on fruit juice. He was very confused with this question as he never even considered peeling the edible skin off of fruit.  When hunting and gathering, Caveman Doctor would be foolish to throw any food away. Plus, the skin is usually the brightest and boldest part of the fruit, and Caveman Doctor knows that bold-colored foods are the healthiest and tastiest. However, when researching fruit and fruit with skin, Caveman Doctor realized the skin in fruit tells us a lot about nutrition in general.
 

Should We Eat Fruits with the Skin On? What About Juice?

 
Grandfather WWII

My grandfather during WWII. He turns 95 in one month and never took a med.

As a young boy my grandfather (who turns 95 in two months and has never taken any medication in his life) would always tell me to eat fruits with the skin on. I thought this was an old wives’ tale passed down for centuries, but he may have been right all along. It seems that not only are fruits and vegetables healthier when eaten with the skin on, but those eaten with the skin on are healthier than those without (berries versus bananas, kiwis versus watermelons, etc.). Cavemen likely never peeled the skin off of fruit and our bodies have adjusted to this over millions of years. While the skin itself has many nutrients in it, fruits and vegetables with intact skin that is edible tend to have more nutrient benefit overall. In fact, the skin from fruit can tell us a lot about nutrition in general.
 

Health Benefits of the Skin on Fruits and Vegetables:

 

1. The skin is mostly fiber, and the more fiber a fruit has, the less your blood sugar levels will spike after eating it.
2. Fiber in the skin helps blunt the release of insulin, a hormone that, when in excess, has been correlated with cancer1-3.
3. Fiber in fruit and vegetables (mostly in the skin) may reduce the risk of colorectal cancer (though fiber from grains likely does not)4.
4. Eating whole fruit with the skin versus juice results in less insulin spikes and decreased hunger afterwards (except for grapes)5.

 
Also, fruits in which the seeds are eaten have more fiber, further slowing glucose digestion and insulin rise.  If you haven’t noticed the pattern yet, the goal is generally to eat more fiber compared to sugar and overall carbohydrates, and any way to maximize this ratio will maximize the health benefits of the foods you are eating.  Insulin is so important in cancer incidence that recent studies have even shown a decreased cancer risk in people taking a drug (metformin) that lowers insulin levels by increasing your cells’ sensitivity to it.6-8 Other ways to increase insulin sensitivity would be to lower carbohydrate and sugar consumption (as BOTH simple and complex carbohydrates cause insulin to increase9), as well as exercising.10 That is our strategy here at CavemanDoctor.com, as we tend to try to avoid taking medications and would rather stay healthy by eating healthy and exercising.
 
The goal is to generally eat more fiber compared to sugar and carbohydrates, and any way to maximize this ratio will maximize the health benefits of the foods you are eating.
 
For instance, consider the nutritional value of a red apple (CLICK on all pictures to enlarge them):

Now compare this to an apple with the skin peeled off:

 

From Peeling the Skin Off of the Apple:

 

1. The amount of fiber is cut in half, while the sugar content stays the same. This causes a greater increase in blood sugar levels in comparison to when the fiber from the skin is eaten.
2. The potassium and vitamin C levels decrease, and the entire amount of folate disappears with the skin.
3. The vitamin A, beta carotene, lutein, and vitamin K all noticeably drop.
4. The level of antioxidants, our free radicals fighters, decreases by a remarkable 500 units!

These vitamins are important for supporting immune function and our body’s natural functions, such as vision.  The drop in the anti-cancer and anti-inflammatory power of antioxidants is huge!  The peel is also a great source of quercetin, an important antioxidant that may decrease inflammation11, 12, the risk blood clots and heart attacks13, 14, and cancer15-17.  To top it off, quercetin and other plant-based antioxidants are found throughout nature, with little to no side-effects and an exceptional safety record18, avoiding the side effects of medications taken for these same health issues.  Basically, the bolder-colored the fruit is (along with eating the peel), the higher the cancer-fighting and healthy antioxidants within.
 
This can be taken one step further when comparing an apple with honeydew, a pale colored fruit in which the skin is always removed prior to eating.
 

 
While eating honeydew is still healthier than eating your best grain source, their antioxidant content still pales in comparison (and color…) to the red apple.  In terms of health benefits and antioxidants, berries blow everyone out of the water.
 
I by no means want you to believe fruits are bad as they supply us with a natural form of many vitamins and nutrients.  I prefer fruits to satisfy my sweet tooth over all grains, starches, sugars, and candies.  That being said, some fruits are better than others, giving you a better bang for your buck.  A simple method is to eat fruits in which the skin can be eaten as well. For instance, bananas and melons, which provide less fiber and antioxidants, cannot be eaten without peeling the skin. As a result, they are not my first choices for fruits. If you are having trouble losing weight, a switch may help you get over the hump.
 
In fact, here is a list of antioxidants for some fruits along with the carbohydrate content (fiber, sugar, and total carbohydrates). Remember, the more fiber and less sugar and total carbohydrates, the better. I even included a total fiber to carbohydrate ratio column. The higher this number the better (the more bang for your buck). This is an easy way to compare how fruits are going to cause an increase in insulin, and whether it’s a little jump or a spike.
 

 
While we are being perfectionists comparing the health values of different fruits, compare these values to that of grain, starches, and sugar-based products. It’s not even close. Also, note the amount of carbohydrates in these foods – the values are through the roof. The amount of carbohydrates that we are able to consume in one sitting when eating grains is astronomical. A large bowel of cereal can often give you near or over 100 grams of carbohydrates. Try eating that many carbohydrates from fruit – it’s much harder. While some people can still overeat with fruit, grains and sugars result in overconsumption far too often and too easily.
 

 
For those of you that like graph form, here is a list of several grains, a starch, fruits, and vegetables. The height of each bar is the total carbohydrate to fiber ratio – the lower the better. Also, take note of the colors of the bars and how they correlate with less overall carbohydrates (red for berries and green for vegetables).
 

 

What About Fruit Juice?

 
Drinking fruit juice is like eating fruit without the peel on steroids. Juicing basically removes the entire bang from the fruit, leaving all buck. This is one of the main reasons why I don’t advocate drinking any fruit juice. While peeling fruit alone removes many vitamins and fiber, juicing it furthers the leaching of vitamins and fiber, leaving a sugary solution with very little fiber (if any) and a massive insulin spike when consumed5 (comparable to drinking soda). Most vitamins are gone as well, and many juices have to actually add vitamin C back in, the vitamin that is naturally present in large amounts in fruit.
 
Also, an apple fills you up much better than a glass of apple juice.  Look here at the nutritional stats on apple juice. Ascorbic acid (vitamin C) is added to juice, raising this level. However, notice each serving has a whopping 24 grams of sugar, no fiber, and barely any iron or calcium. The nutritional value of apple juice is not even comparable to an apple. Drinking juice is basically drinking sugar water and bombing your blood with loads of glucose, and we all know what that does to your insulin.
 

In Summary:

 
Peeling the skin off of fruit also peels away many of its health benefits, leaving unchecked amounts of sugar and carbohydrates. This is the same thing that happens when we eat sugary foods and grains – we consume large amounts of unchecked carbohydrates. Fruit with the skin on is a great model for how the rest of our diet should be, in the sense that Nature made it right. Old Mother Nature threw tons of vitamins in the peel and more antioxidants in the bold-colored foods that caught the eye of Caveman Doctor and his people. The path to good health may be easier than we think.
 
*All values in graphs from The USDA Nutrient Database
 

References:

1. Iwamura M, Sluss PM, Casamento JB, Cockett AT. Insulin-like growth factor I: action and receptor characterization in human prostate cancer cell lines. The Prostate 1993;22(3): 243-52.

2. Macaulay VM. Insulin-like growth factors and cancer. British journal of cancer 1992;65(3): 311-20.

3. Rubin R, Baserga R. Insulin-like growth factor-I receptor. Its role in cell proliferation, apoptosis, and tumorigenicity. Laboratory investigation; a journal of technical methods and pathology 1995;73(3): 311-31.

4. Terry P, Giovannucci E, Michels KB, et al. Fruit, Vegetables, Dietary Fiber, and Risk of Colorectal Cancer. Journal of the National Cancer Institute 2001;93(7): 525-33.

5. Bolton RP, Heaton KW, Burroughs LF. The role of dietary fiber in satiety, glucose, and insulin: studies with fruit and fruit juice. The American journal of clinical nutrition 1981;34(2): 211-7.

6. Evans JMM, Donnelly LA, Emslie-Smith AM, Alessi DR, Morris AD. Metformin and reduced risk of cancer in diabetic patients. BMJ 2005;330(7503): 1304-05.

7. Libby G, Donnelly LA, Donnan PT, Alessi DR, Morris AD, Evans JM. New users of metformin are at low risk of incident cancer: a cohort study among people with type 2 diabetes. Diabetes care 2009;32(9): 1620-5.

8. Landman GWD, Kleefstra N, van Hateren KJJ, Groenier KH, Gans ROB, Bilo HJG. Metformin Associated With Lower Cancer Mortality in Type 2 Diabetes. Diabetes care 2010;33(2): 322-26.

9. Crapo PA, Reaven G, Olefsky J. Plasma glucose and insulin responses to orally administered simple and complex carbohydrates. Diabetes 1976;25(9): 741-47.

10. Borghouts LB, Keizer HA. Exercise and insulin sensitivity: a review. International journal of sports medicine 2000;21(1): 1-12.

11. Comalada M, Camuesco D, Sierra S, et al. In vivo quercitrin anti-inflammatory effect involves release of quercetin, which inhibits inflammation through down-regulation of the NF-κB pathway. European Journal of Immunology 2005;35(2): 584-92.

12. Morikawa K, Nonaka M, Narahara M, et al. Inhibitory effect of quercetin on carrageenan-induced inflammation in rats. Life Sciences 2003;74(6): 709-21.

13. Pace-Asciak CR, Hahn S, Diamandis EP, Soleas G, Goldberg DM. The red wine phenolics trans-resveratrol and quercetin block human platelet aggregation and eicosanoid synthesis: Implications for protection against coronary heart disease. Clinica Chimica Acta 1995;235(2): 207-19.

14. Hertog MGL, Feskens EJM, Kromhout D, Hollman PCH, Katan MB. Dietary antioxidant flavonoids and risk of coronary heart disease: the Zutphen Elderly Study. The Lancet 1993;342(8878): 1007-11.

15. Jeong J-H, An JY, Kwon YT, Rhee JG, Lee YJ. Effects of low dose quercetin: Cancer cell-specific inhibition of cell cycle progression. Journal of Cellular Biochemistry 2009;106(1): 73-82.

16. Lamson DW, Brignall MS. Antioxidants and cancer, part 3: quercetin. Alternative medicine review : a journal of clinical therapeutic 2000;5(3): 196-208.

17. Murakami A, Ashida H, Terao J. Multitargeted cancer prevention by quercetin. Cancer Letters 2008;269(2): 315-25.

18. Middleton E, Kandaswami C, Theoharides TC. The Effects of Plant Flavonoids on Mammalian Cells:Implications for Inflammation, Heart Disease, and Cancer. Pharmacological Reviews 2000;52(4): 673-751.


 
© 2015 CDR Health and Nutrition, LLC. All Rights Reserved

9 Comments

  1. cn

    Very nice pic of your grandfather! He must be very proud of you.

    Reply
  2. CavemanDoctor (Post author)

    Thank you very much!!

    -CD

    Reply
  3. Design

    Really good post! Thanks for the information.

    Reply
    1. cavemandoctor (Post author)

      Thanks! Glad the info was useful!

      Reply
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