Wednesday, February 2, 2011

To Cook Or Not To Cook - The Raw Food Dilemma


It is widely known that eating more fruits and vegetables is better for your overall health and it's not just grandma saying this anymore.  The recently published and updated 2010 Dietary Guidelines for Americans stated this and even dedicated two full pages pointing out the benefits of a plant-based diet for one's health [1]. But is eating a raw food diet better than eating a diet with some cooked foods in it?

This claim has been made by many raw-foodists as they say eating a diet devoid of any cooked foods or at least eating only a minimal amount of cooked food is the only way to achieve optimal health.  To be considered a raw food diet one must consume 75% or more of their food raw.  Some raw-foodists say that eating a 100% raw diet is the only way to achieve perfect health.  So what's the right answer?

Unfortunately, this is not an easy topic to paint a clear black and white picture about and no long term studies are available to date to adequately determine whether a raw food diet is superior for one's overall health.  If anything there seems to be pros and cons to both sides.  Let's take a look at what the scientific world has to say about all of this.

Are cooked foods more toxic?

Many raw food advocates claim that cooked foods are toxic and therefore should not be consumed.  While they do have some good points regarding the formation of certain carcinogens and other toxic agents in cooked foods it appears that the method of cooking plays a significant role in all of this.

▸  Heterocyclic Amines (HCAs)
    ▪  Defined as chemicals that are formed when amino acids (building blocks of protein), sugar, and 
        creatinine/creatine react with one another at high temperatures [2].  Creatinine and creatine are
        found in meat and therefore HCAs are only formed and eaten when consuming the flesh 
        of an animal or fish.
    ▪  The higher the temperature and the longer the meat is cooked for play a significant role in the 
        formation of HCAs.  Frying, broiling, baking, and grilling will all increase the formation of HCAs 
        especially above 300℉ [3,4,5].
    ▪  HCAs have been shown to be mutagenic which means they can cause mutations and damage DNA 
        [6].  This may increase one's risk of cancer and numerous epidemiological studies have linked a 
        high consumption of well-done, fried, or barbecued meats to an increased risk of colorectal cancer, 
        breast cancer, prostate cancer, and pancreatic cancer [7,8,9,10,11].

▸  Maillard molecules
    ▪  Many raw-foodist say that Maillard reactions (reactions between a protein and carbohydrate) 
        of the chemicals".  This claim is made, of course, without any long term scientific data providing 
        any proof of this.
    ▪  Maillard reactions are responsible for a portion of the browning effect and flavoring of different 
        food products [12].
    ▪  Maillard molecules are not just produced in foods but also via non-food pathways in the human 
        body when collagen and free sugars undergo cross-linking to produce Advanced Glycation 
        Endproducts (AGE's) which occur at an advanced stage of a Maillard reaction [13].  In
        diabetic patients this reaction is accelerated due to elevated blood sugar and has led to tissue 
        degeneration.  Diabetics also have decreased kidney function which has been shown to reduce the 
        clearance of AGE's from the body leading to increased renal-vascular injury [14].  However, these 
        damaging effects don't seem to occur in non-diabetic patients.
    ▪  Consuming a diet rich in Maillard reaction products has actually been shown to have antioxidant 
        effects in vitro (in test tube laboratory experiments) and has also been shown to reduce oxidative 
        damage to LDL (bad cholesterol) but it still remains to be seen in vivo (in living organisms) [15].

▸  Polycyclic Aromatic Hydrocarbons (PAHs)
    ▪  PHAs are carcinogens formed when meats are grilled over an open flame or by smoking meat 
        products [3,16].  They are also found in car exhaust fumes, polluted air, and cigarette smoke.
    ▪  An increase in the incremental lifetime cancer risk of individuals has been shown in those who have 
        a higher daily dietary exposure to PHAs [17].

▸  Acrylamides
    ▪  Found in moderate amounts in heated protein-rich foods and in high amounts in cooked 
        carbohydrate-rich foods such as potatoes, potato chips, beetroot, and crisp bread [18].
        Acrylamides are not found, however, in unheated or boiled foods [18].
    ▪  Acrylamides have shown mixed results with being a possible carcinogen in humans.  
        Epidemiological studies have shown an increased risk of ovarian and endometrial cancer, renal cell 
        cancer, breast cancer, and oral cavity cancer when exposed to higher levels of acrylamides but a 
        decreased risk in lung and bladder cancer in women and prostrate and oro- and
        hypopharynx cancer in men [19].

As you can see from above there are many different factors that go into the potential toxicity of foodstuffs.  It appears from reviewing the scientific data that cooking foods for longer periods of time at higher temperatures can lead to increased exposure to potential toxins.  In contrast, using water based cooking methods such as boiling or steaming reduces or eliminates these risks. 

In addition, it is also clear that consuming a plant-based diet and limiting or avoiding meat products all together will dramatically reduce your exposure to potentially harmful carcinogens such as HCAs and PAHs.  The benefits of increasing health promoting vegetables in one's diet was shown to be the case in a review of 28 studies on the consumption of raw vs. cooked vegetables and cancer risk.  It showed that increasing your consumption of vegetables in general whether raw or cooked led to a decreased risk of several different types of cancer [21].

Do Cooked Foods Contain Less Nutrition?

Another claim by raw food advocates is that when you cook food you destroy the nutrients and enzymes in food that make them worth eating in the first place.  This topic of interest has some valid points to it.  As you will see below a portion of vitamins and minerals are lost in cooked foods but this is not always the case.  The debate whether an essential role is played by enzymes contained within raw foods will also be discussed.

▸  Vitamin C tends to be one of the vitamins that is most affected by cooking.  Depending on cooking 
    method and cooking ware used a loss of anywhere from 18%-60% can be seen when cooking frozen 
    vegetables [20].
▸  One study looked at the effects of heating tomatoes and showed an increase in total antioxidant 
    activity and in lycopene content despite a loss in vitamin C [22].  It also showed no significant 
    changes in the amount of two powerful antioxidant classes known as phenolics and flavonoids.
▸  Cooking carrots has been shown to increase the availability of carotenoids [23].  One study showed 
    an increase from 3% to 27% in beta-carotene content in raw vs. cooked carrots [24].
▸  Different cooking methods was shown to make a different in total antioxidant capacity in cooking the 
    following vegetables - carrots, courgettes (zucchini), and broccoli.  Boiling, steaming, and frying were 
    all tested.  Frying showed the least amount of retained antioxidants while water based methods 
    preserved more antioxidant compounds particularly the carotenoids [25].
▸  One review of the vitamin and mineral content of raw vs. cooked foods showed a 10-25% overall loss 
    of vitamins in cooked foods with only a negligible loss of minerals.
▸  Many raw-foodists claim that enzymes found in the plant food that you eat is used to help digest this 
    food thereby preserving your own body's supply of enzymes.  However, it has been shown that 90% 
    of all nutrients are absorbed in the small intestine and that the majority of the plant
    enzymes consumed in foods we eat are destroyed in the stomach before the food gets to the small 
    intestine and this food is then broken down by the body's own bile and pancreatic enzymes [26].

It is apparent that eating both raw and cooked foods has it's pros and cons in regards to the nutritional value of the foods being consumed.  Again water based cooking methods have been shown to minimize the loss of vitamins and minerals.  In some cases steaming or boiling can even lead to an increase in the amount of certain antioxidants in select foods.

Another important point to make here is that you can increase the amount of vegetables that you eat in your diet by simply cooking them.  This softens the food and makes it easier to consume.  Including steamed veggies or a vegetable based soup in one of your daily meals can easily increase your intake of those all important disease fighting phytochemicals and antioxidants that we never seem to get enough of.  Eating a 100% raw diet makes it difficult to eat as much of these bulkier foods and those who do eat this way rely heavily on fruit to make up a majority of their diet.  I'm not saying that fruit is a bad thing but rather that it's important to maintain a balanced approach in your dietary habits by consuming a wide variety of plant-based foods to meet your nutritional needs.

Don't get me wrong eating raw foods is important and you should try to get at least 50% of your calories this way if possible.  But eating a completely raw diet has not been shown in long term studies to be superior.  If I missed this data then by all means please comment and share these findings for the benefit of all who read this.  If anything an all raw diet has been shown to increase dental erosions [27] and decrease overall bone mass [28] in individuals over the long term.  Finally, the most important thing you can do for your overall health is include plenty of nutrient dense, plant based foods and reduce or eliminate animal based foods in your diet.  This has been shown in numerous studies to decrease your risk of chronic diseases and give you more health and vitality as you go throughout life.  I'll leave you with a link to a well done 3 part review article of raw food diets and two short videos discussing a raw food diet for those who are interested in exploring this topic further.
















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References:
1 U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2010. 7th Edition, Washington, DC: U.S. Government Printing Office, December 2010.
2 Skog K, Johansson M, Jägerstad M. Factors affecting the formation and yield of heterocyclic amines. Princess Takamatsu Symp. 1995;23:9-19.
3 Cross AJ, Sinha R. Meat-related mutagens/carcinogens in the etiology of colorectal cancer. Environmental and Molecular Mutagenesis 2004; 44(1):44–55.
4 Jägerstad M, Skog K. Formation of meat mutagens. Adv Exp Med Biol. 1991;289:83-105.
5 Knize MG, Dolbeare FA, Carroll KL, et al. Effect of cooking time and temperature on the heterocyclic amine content of fried beef patties. Food Chem Toxicol. 1994 Jul;32(7):595-603.
6 Sinha R, Kulldorff M, Chow WH, et al. Dietary Intake of Heterocyclic Amines, Meat-derived Mutagenic Activity, and Risk of Colorectal Adenomas. Cancer Epidemiol Biomarkers Prev May 2001 10; 559.
7 Cross AJ, Ferrucci LM, Risch A, et al. A large prospective study of meat consumption and colorectal cancer risk: An investigation of potential mechanisms underlying this association. Cancer Research 2010; 70(6):2406–2414.
8 Schiffman M. H., Felton J. S. Refried foods and the risk of colon cancer. Am. J. Epidemiol. 1990; 131: 376-378.
9 Norrish A. E., Ferguson L. R., Knize M. G., Felton J. S., Sharpe S. J., Jackson R. T. Heterocyclic amine content of cooked meat and risk of prostate cancer. J. Natl. Cancer Inst. 1999; 91: 2038-2044.
10 Sinha R, Park Y, Graubard BI, et al. Meat and meat-related compounds and risk of prostate cancer in a large prospective cohort study in the United States. American Journal of Epidemiology 2009; 170(9):1165–1177.
11 Zheng W, Lee SA. Well-done Meat Intake, Heterocyclic Amine Exposure, and Cancer Risk. Nutr Cancer. 2009; 61(4): 437–446.
12 Ames J. Control of the Maillard reaction in food systems. Trends in Food Science and Technology. 1990; (1); 150-154.
13 NIH Conference on the Maillard Reaction in Aging, Diabetes, and Nutrition, & Monnier, Vincent M. & Baynes, John W.  1989  The Maillard reaction in aging, diabetes, and nutrition : proceedings of an NIH Conference on the Maillard Reaction in Aging, Diabetes, and Nutrition, held in Bethesda, Maryland, September 22-23, 1988 / editors, John W. Baynes, Vincent M. Monnier  A.R. Liss, New York.
14 Koschinsky T, He CJ, Mitsuhashi T, et al. Orally absorbed reactive glycation products (glycotoxins): an environmental risk factor in diabetic nephropathy. Proc Natl Acad Sci U S A. 1997 Jun 10;94(12):6474-9.
15 Dittrich R., Dragonas C., Kannenkeril D., Hoffmann I., Mueller A., Beckmann M.W., Pischetsrieder M. A diet rich in Maillard reaction products protects LDL against copper induced oxidation ex vivo, a human intervention trial. Food Research International. 2009; 42 (9), pp. 1315-1322.
16 Gomaa EA, Gray JI, Rabie S, Lopez-Bote C, Booren AM. Polycyclic aromatic hydrocarbons in smoked food products and commercial liquid smoke flavourings. Food Addit Contam. 1993 Sep-Oct;10(5):503-21.
17 Xia Z, Duan X, Qiu W, et al. Health risk assessment on dietary exposure to polycyclic aromatic hydrocarbons (PAHs) in Taiyuan, China. Sci Total Environ. 2010 Oct 15;408(22):5331-7.
18 Tareke E, Rydberg P, Karlsson P, Eriksson S, Törnqvist M. Analysis of acrylamide, a carcinogen formed in heated foodstuffs. J Agric Food Chem. 2002 Aug 14;50(17):4998-5006.
19 Hogervorst JG, Baars BJ, Schouten LJ, et al. The carcinogenicity of dietary acrylamide intake: a comparative discussion of epidemiological and experimental animal research. Crit Rev Toxicol. 2010 Jul;40(6):485-512.
20 Nursal B, Yücecan S. Vitamin C losses in some frozen vegetables due to various cooking methods. Nahrung. 2000 Dec;44(6):451-3.
21 Link LB, Potter JD. Raw versus cooked vegetables and Cancer Risk. Cancer Epidemiol Biomarkers Prev September 2004 13; 1422.
22 Dewanto V, Wu X, Adom KK, et al. Thermal Processing Enhances the Nutritional Value of Tomatoes by Increasing Total Antioxidant Activity. J. Agric. Food Chem., 2002, 50 (10), pp 3010–3014.
23 Talcott ST, Howard LR, Brenes CH. Antioxidant Changes and Sensory Properties of Carrot Puree Processed with and without Periderm Tissue. J. Agric. Food Chem., 2000, 48 (4), pp 1315–1321.
24 Hedrén E, Diaz V, Svanberg U. Estimation of carotenoid accessibility from carrots determined by an in vitro digestion method. Eur J Clin Nutr. 2002 May;56(5):425-30.
25 Miglio C, Chiavaro E, Visconti A, et al. Effects of Different Cooking Methods on Nutritional and Physicochemical Characteristics of Selected Vegetables. J. Agric. Food Chem., 2008, 56 (1), pp 139–147.
26 Tortora GJ, Anagnostakos NP Principles of Anatomy and Physiology, 1981 Harper and Row, New York. p. 629.
27 Ganss C, Schlechtriemen M, Klimek J. Dental erosions in subjects living on a raw food diet. Caries Res. 1999;33(1):74-80.
28 Fontana L, Shew JL, Holloszy JO, Villareal DT. Low bone mass in subjects on a long-term raw vegetarian diet. Arch Intern Med. 2005 Mar 28;165(6):684-9.

1 comment:

  1. GREAT article Dustin! I have so much to learn on this subject but you really put this in simple terms for me to understand.

    We recently bought a blendtech and finally the kids are eating spinach and tons of vegi's without gagging them down- love that thing and definitely worth the investment. I know raw is better in most instances and this has made it achievable for us.

    Thanks for your help and explanation in this subject!

    ReplyDelete