Put Down That Kale Smoothie – Why You Should Cook Your Food

I hear and read about lots of people making kale smoothies, consuming raw nuts, and munching salads consisting of raw broccoli. So, I decided to take a look at some research to see what the nutritional costs are to eating raw foods. The truth is, it’s better for your body to consume primarily cooked or lacto-fermented vegetables.

Much of the current food science research suggests that cooking food increases the nutrients available from vegetables, meat and fish in humans. Some of the benefits include: improved digestibility of plants, less energy spent on digesting and absorbing food, and most importantly, killing dangerous pathogens present in meat and to some extent, plant matter. Non-thermal processing of food also seems to improve the bioavailability of nutrients, digestibility and even increase the total health benefits of certain foods.


Food has been heat-treated for many centuries, since our ancestors learned, by trial and error, to master fire for cooking purposes approx. 700,000 years ago, to modify the taste and preserve nutritional properties of foods. The invention and continuous development of food treatment has had a substantial, if not major impact on the intellectual, societal and economic development of mankind. The health benefits of fermentation have been known for centuries. In 76 A.D., the Roman historian Plinio advocated the use of fermented milks for treating gastrointestinal infections.


Cooking enhances digestibility of vegetables

Cooking also inactivates anti-nutritional factors such as protease inhibitors and other natural toxins. The second effect is enhanced digestibility of food and bioavailability of nutrients. For example, gelatinization of starch makes possible its hydrolysis by amylase enzymes. Destruction of cell walls in vegetables improves the bioavailability of compounds such as carotenoids and polyphenols. Nuts and seeds contain many anti-nutrients in their raw state. Soaking your nuts overnight, then dehydrating them in a dehydrator or low heat oven will increase the bioavailability of the nutrients in nuts and seeds. Certain foods are associated with disrupted thyroid hormone production. Foods belonging to the cruciferous family are called “crucifers,” and include broccoli, kale, cauliflower, Brussels sprouts, cabbage, mustard, kohlrabi, and turnips. These foods appear to reduce thyroid function by blocking thyroid peroxidase, and also by disrupting messages in thyroid cells. Cooking these vegetables greatly reduces these negative effects.


1319136025_982fa64ad8caEating raw food has a cost

The thermic effect of food (TEF) is defined as the increase in metabolic rate after ingestion of a meal, due to energy spent on digestion, absorption and metabolizing nutrients. Cooking also appears to have a positive effect on net energy in the body. Humans on vegetarian diets exhibit higher reproductive performance when eating cooked food than raw food. Evidence of low energy intake in women eating predominantly raw food is supported by their having higher rates of amenorrhea or menstrual irregularities than those eating cooked food.  In one study, it was found that menstruation was absent in 23% of females of childbearing age who ate at least 70% of their food raw and in 50% of women reporting a 100% raw diet. Although these women were primarily vegetarian, the addition of raw meat to the diet did not change the odds of ovarian suppression. The researchers concluded that women suffered because of their relatively low net energy gain as a consequence of  eating their food raw.  In another study, a nutritional analysis suggested that in traditional communities, a diet of raw wild foods would render survival and reproduction difficult.


Higher fat meats can lead to better energy balance

It is important to note that eating cooked very lean meats has a nutritional cost. Archaeological evidence suggests that fat derived from bone marrow may have been preferred over muscle tissue as a source of energy and nutrients among early humans. Diets deriving more than 50% of calories from lean protein can lead to negative energy balance, so-called ‘‘rabbit starvation,’’ due to the high metabolic costs of protein digestion.


Cooking kills pathogens

Cooking kills foodborne bacteria, including strains associated with raw meat products such as Escherichia coli, Salmonella, Campylobacter, Staphylococcus, and Listeria. The potential energy savings due to reduced immune maintenance and upregulation could be sizeable. Raw wild meat is possibly less pathogen-bearing on average than raw meat that has been raised and processed for mass-market consumption. When meat is processed at the slaughterhouse, ecoli and other pathogens from the intestines can invade the ground meat. This is why most outbreaks involve burgers and other forms of ground meat but is not usually associated with steaks. These pathogens do not enter the inside of the muscle tissue (steaks). When eating industrially raised red meat, it is suggested to cook burgers well.  New processing techniques in industrial meat facilities, such as piercing steaks to improve texture of tougher cuts of meat, can mean that pathogens may be entering steaks as well as burgers. Slow cooking meat appears to be one of the best methods to prepare meat for optimal digestibility.


Lighly cooked fish is healthier than raw or fried

In the case of fish, it appears that lightly cooked is optimal. In one study where edible portions of fresh fish were used raw, fried, cooked and undercooked, the researchers concluded that the breakdown of fish proteins were all fairly complete, but general digestibility was greatest with underdone fish as compared to raw, fully cooked or fried fish.


Fermentation improves gut flora

Fermentation is a non-thermal process that produces chemical changes by enzymes produced from bacteria, microorganisms or yeasts and is one of the oldest known food preservation techniques. During fermentation, the carbohydrate energy source in food, such as lactose in milk is converted to lactic acid. The same happens when pickles are produced from cucumbers. Yeasts convert glucose to ethanol and carbon dioxide. Many health-producing secondary metabolites are produced through fermentation, especially B vitamins and bioactive peptides which can be antimicrobial and immune-stimulatory. In the early 1900s it was realized that bifidobacteria may be effective in preventing infection in infants and the consumption of fermented milks were seen to reverse putrefactive effects of the gut micro flora, leading to the development of the probiotic concept. Probiotics are now used in the treatment of infections and used to promote a healthy immune system. Consuming fermented foods will improve the presence of healthy bacteria in the gut.


Pounding, curing and cooking meat is beneficial

When considering meat, there seems to be some evidence that processing meat either by pounding, drying, curing or cooking is beneficial. Pounding meat and making it soft seems to reduce the cost of digestion, partly because it can pass more quickly through the gut. T

he collagen surrounding each fascicle of muscle fibers generally remains too tough for mastication until heated to 60–70 C, when collagen begins to be hydrolyzed into gelatin, a soluble protein. Although the muscle fibers themselves remain tough, eat meat cooked beyond this temperature leads to gelatinization of the collagen, which separates the muscle fibers and the gelatin.


Improved texture means we eat more protein

Improved texture of meat makes it easier to chew, and easier for our bodies to break down. Also when the fats are heated to oil from a fat, it’s easier for bile to emulsify and ultimately leads to faster absorption. In studies, humans and chimps prefer the taste of cooked meat, leading to us eating more of it. Consumption of more protein meant larger brains and bigger muscles as we evolved.


In summary, it appears that cooking meat and vegetables, consuming lacto-fermented vegetables, and other cured meat is preferable to raw. Well cooked poultry and red meat is safest and easiest to break down, in addition to tasting better. It also appears that the leanest cuts may not be the healthiest to focus on for the bulk of the diet. Regarding fish, lightly cooked fish seems to be optimal, based on the research. Finally, cooking and other methods which improve the texture of meat, make it more palatable leading us to consume more of it. Some studies indicate that our brain size grew at the same time humans discovered fire, and one theory states this could be due to increased protein consumption at that time.




Barham, P., 2001. The Science of Cooking. Springer, Berlin.

Blumenschine, R.J., Hominid carnivory and foraging strategies, and the socioeconomic function of early archaeological sites. Phil. Trans. R. Soc. Lond., 1991, Series B 334, 211–221.

Blumenschine, R.J., Madrigal, T.C., Variability in long bone marrow yields of East African ungulates and its zooarchaeological implications. J. Archaeol. Sci. 1993 20, 555–587.

Carmody, Rachel N.; Wrangham, Richard W., The energetic significance of cooking. Journal of Human Evolution 2009, 57, 379–391.

Evenepoel, P., Geypens, B., Luypaerts, A., Hiele, M., Rutgeerts, P., Digestibility of cooked and raw egg protein in humans as assessed by stable isotope techniques. J. Nutr. 1998, 128, 1716–1722.

Halton, T.L., Hu, F.B., The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review. J.Am. Coll. Nutr. 2004, 23, 373–385.

Koebnick, C., Strassner, C., Hoffmann, I., Leitzmann, C.,  Consequences of a long-term raw food diet on body weight and menstruation: results of a questionnaire survey. Ann. Nutr. Metab. 1999, 43, 69–79.

Laden, G., in: Eisenbrand, G., Engel, K.-H., Grunow, W., Hartwig, A., Knorr, D., Knudsen, I., Schlatter, J., Schreier, Thermal Processing of Food: Potential Health
Benefits and Risks. Deutsche Forschungsgemeinschaft (DFG)-Symposium, 2006, Senate Commission on Food Safety (SKLM).

Oka, K., Sakuarae, A., Fujise, T., Yoshimatsu, H., Sakata, T., Nakata, M., Food texture differences affect energy metabolism in rats. J. Dent. Res. 2003, 82, 491–494.

Saha, K.C. The Effect of boiling and frying on the enzymic hydrolysis of fish protein. Journal of the Indian Chemical Society. 194017, 259-63.

Speth, J.A., Spielmann, K.A., Energy source, protein metabolism,and huntergatherer subsistence strategies. J. Anthropol. Archaeol. 1983, 2, 1–31.

Van Boekel, Martinus; Fogliano, Vincenzo; Pellegrini, Nicoletta; Stanton, Catherine; Scholz, Gabriele; Lalljie, Sam; Somoza, Veronika; Knorr, Dietrich; Rao Jasti, Pratima; Eisenbrand, Gerard, A review on the beneficial aspects of food processing. Mol. Nutr. Food Res. 2010, 54, 1215–1247.

Wrangham, R., 2009. Catching Fire: How Cooking Made Us Human. Basic Books, New York, NY.


  • http://www.facebook.com/people/Valerie-Jaquith/100000785493600 Valerie Jaquith

    This is a great article and well informed! Thank you! A video lecture at http://vimeo.com/27570335 “An Organic Chemist’s Perspective on Paleo” by Mathieu Lalonde, PhD was very informative on this subject! Very heavy on the sceince. I loved it. Thanks for this timely post!

    • diana

      Yes, Mat is a friend of mine and sent me the research for this post. Thanks!

    • Anonymous

      Thanks Valerie – Mat is actually a good friend and sent me the research articles.

  • http://www.facebook.com/tribe2012 John Dodge

    This article is extremely flawed in its approach. It deals with life style of managed people living in cities or farms – not indigenous humans living in their native habitat the tropics. Meat has only become popular to ward off malnutrition caused by high flour and grain intake of class based societies. Human food consists primarily of fruit and leaves with the addition of fish as you venture farther away from the tropics. Any other diets can be traced to the managed care of the empire builders.
    Most of this (commercial food) “science” comes from using the terrible colonial life style imposed on the native people of Europe by the Roman Empire as the base level of natural human diet and then showing how modern “civilized” management saved these people and increased their quality of life.
    No where do these “scientists” consider the thousands of years of healthy balanced life style of Indians in America, Europe and Asia and of course the most neglected people – the tropical villagers of Africa.

    • Colleen K. Peltomaa

      Well written. I’ve recently started eating mostly fruits and vegetables (raw and cooked), dropping the grains and seeds and meats for the most part. I find that the fruits have a de-toxing effect and can see how they can reverse dis-ease trends of the body.

      There are hardly any peoples remaining who live naturally, even in the tropics where fruiting trees abound.

      I’ve been watching Dr. Robert Morse, ND on Youtube and that is partly what convinced me to change to eating mostly raw fruits and vegetables.

      I think it was important that you pointed out how politics and the master-slave games have perverted our diets worldwide.

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  • Anonymous

    The studies I reference in my article, “Why you should cook your food” are to illustrate specifically the difference in health consequences between cooked and raw food. If you are looking to see studies on native populations where they are not eating “European” food, please refer to the work of Staffan Lindeberg on the Kitava population. http://www.staffanlindeberg.com/TheKitavaStudy.html
    You might also be interested in the work of Dr. Weston A. Price in his book, “Nutrition and Physical Degeneration”.
    Some populations do survive little protein but I’ve not heard of a native population that was completely vegetarian. Even though some cultures seem to survive on sub-optimal food sources, I’m interested in what it optimal for human health. Based on the research I’ve seen, it appears that eating primarily cooked vegetables and protein seems to be optimal.

    • Engelhafen .

      You make a false assumption when you equate vegetarianism with low protein. The highest protein content food per gram is watermelon seeds, and per weight, spinach has more protein than a steak does.

      • Nutritional_Therapist

        Nutrition 101: animal protein is more bioavailable than plant protein. I’m not assuming anything here – this is science.

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  • Anonymous

    There is no enzyme activity in cooked food. Eating meat raises the risk for cancer in the body,osteo-arthritis,bone degeneration and heart issues.
    Read … The China Study by T Colin Campbell. 
    Excellent book.

    • Anonymous

      I’m very familiar with The China Study and I really enjoy this response to it: http://rawfoodsos.com/2010/08/03/the-china-study-a-formal-analysis-and-response/ by Denise Minger. There seems to be more than one flaw in the logic from the China Study.

    • Julianne Taylor

      I’ve noticed that many vegans have a thing about enzymes in food. And if we don’t get them we won’t be able to digest our food properly. There is also a theme that we have a bank full of enzymes and they run out eventually.
      Totally flawed scientifically, we make enzymes on an as needed basis as we digest food. We are constantly making them as we do all the other proteins in our body.

      • Diana Paez

        Where is the research that supports your claim that it is flawed “scientifically”? I’ve read more than a few books on this subject that contain peer reviewed studies that support ‘the thing vegans have about enzymes’.

        Explain why this 70 year old woman that has been eating raw for 30 years looks younger and healthier than most 40-50 year old women I know.

        Read the book Enzyme Nutrition by Dr. Edward Howell so you can find all the information and studies you want about this.

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  • Anonymous

    Very interesting article. Thanks! I do eat raw meat several times a week and I incorporate raw foods in each meal, usually veggies, eggs, or dairy. I think it is a good idea to get both cooked and raw foods in the diet. Price found that most cultures used both raw and cooked foods. 

    Another option is to juice veggies, fruit, and organ meats. This is a great way to incorporate nutrient-dense raw food without the worries on digestion. I juice beef liver 1x/week and I juice veggies and fruits several times/week. The juice feels great to me!

    But I do love cooked meat as well and I always cook meat slow and low. 

    Also, I want to mention that we are all different and some people tolerate raw foods better than others. Observing the body is key!

  • luke murray

    There seems to be loads of misinformation here… Going on personal experience after eating a 100% raw diet for over 7 yrs including raw fatty meat everyday for 5 and now 2+ of mainly raw fatty meat and raw dairy, my health has only improved. Body cleanses itself naturally, with increased sustainable energy levels and most importantly, feeling grounded.
    Here is a thought… we don’t need roughage to keep our bowels moving,
    we need bacteria. Those lovely little helpers that the mainstream
    conditions us to fear. Fear not, as there are many, many people out
    there eating an all raw meat diet and thriving with the help of E-coli and friends!

    • diana

      I’m glad you feel good eating raw meat. I’m not sure what you mean about “loads of misinformation here” are you talking about my post? I have backed it up with scientific studies stating how cooked foods are optimal. Raw meat is ok, but the risks of contamination are high, the proteins are more difficult to break down and the fats are actually easier for our bodies to absorb in the cooked form based on what I read. You need to consume much more raw meat than cooked meat in order to obtain the same nutrients. I’m interested in the optimal diet for humans. Please take some time to read the studies I’ve referenced before calling it misinformation. N=1 is not proof that a raw diet is optimal. A lot of people on raw food diets feel good initially because they are eliminationg much of the foods that I also advocate removing (gluten, grains, processed foods, sugars, etc). However, after some time, their health declines, they lose muscle mass and end up getting sick. Many of my nutrition clients are ex-raw foodists. All this being said, I’m happy that you feel that it’s working for you.

    • Anonymous

      I’m glad you feel good eating raw meat. I’m not sure what you mean about “loads of misinformation here” are you talking about my post? I have backed it up with scientific studies stating how cooked foods are optimal. Raw meat is ok, but the risks of contamination are high, the proteins are more difficult to break down and the fats are actually easier for our bodies to absorb in the cooked form based on what I read. You need to consume much more raw meat than cooked meat in order to obtain the same nutrients. I’m interested in the optimal diet for humans. Please take some time to read the studies I’ve referenced before calling it misinformation. N=1 is not proof that a raw diet is optimal. A lot of people on raw food diets feel good initially because they are eliminationg much of the foods that I also advocate removing (gluten, grains, processed foods, sugars, etc). However, after some time, their health declines, they lose muscle mass and end up getting sick. Many of my nutrition clients are ex-raw foodists. All this being said, I’m happy that you feel that it’s working for you.

      • Diana Paez

        Are your really implying that the loss of muscle mass is because of eating raw?

        • Nutritional_Therapist

          I’m not implying this, it’s clearly stated in my post. I’ve referenced this in my article if you’d like to check the references and read the papers.

          • Diana Paez

            Did your patients work out / use their muscles? Because I’ve seen amazing muscular, super fit & toned bodies with years of a 100% LOW FAT raw diet. I’m almost 100% sure physical activity has a lot to do with this too – not just diet. Doug Graham recommends muscle training at least 3 times a week with this diet. How does a gorilla or bonobo which are most physiologically similar to our species keep their muscle mass intact by eating their own natural foods? Perhaps these patients you speak of that get sick and weak are eating raw but too much overt fats and too much proteins (pates, nut spreads, etc. and not enough carbohydrates from fruits and vegetables). Have you read 80 10 10? 80-10-10 makes total sense to me as the optimal diet for the human species.

          • Nutritional_Therapist

            Yes, I speak with all of my clients about their lifestyle including working out.

          • Diana Paez

            I’m sure you do, but that’s not what I’m asking. I’m asking if the patients that you said lost muscle mass were doing weight training during the time they were eating raw foods? How much fats and how much proteins were they eating? I don’t think it’s necessary to cook food at all to prevent sickness and loss of muscle mass. What’s important is getting in the correct ratio of carbohydrates, fats and proteins from the cleanest sources (organic, raw, local).

            Have you read 80-10-10? What’s your take on that?

          • Nutritional_Therapist

            There are many different macronutrient ratios that work for different people. Depending on their needs (an athlete vs a sedentary elderly person) ideal ratios vary quite a bit. I don’t think there is one ratio that is ideal for all humans. What is ideal in my opinion is food quality. Yes, I’ve seen athletic clients who were raw vegans and benefited quite dramatically from eating cooked vegetables and meat. I’m glad you have found something that works for you. Best of luck.

  • Anonymous

    Excellent post! I’ve shared this with many clients because I could not have stated it better myself. Question regarding eating crucifers raw. Since cabbage falls into that category, and kraut and kimchi are technically raw, what’s your stance there? Does the fermentation of those two null and void the  thyroid disruption that raw crucifers can induce? I’d love your feedback. Thanks so much! 

    • Anonymous

      Kraut and kimchi are not really “raw” but fermented. The fermentation actually increases the thyroid damaging components in cabbage. I like saurkraut that contains seaweed in it to counteract the goitrogens in the cabbage. There are lots of recipes online or you can buy it here http://www.culturedvegetables.net/product.sc?productId=2&categoryId=1 

  • Anonymous

    It takes some time until your digestion adapts and upregulates to properly digest raw foods, which is why most of those studies find that you get less nutrition from raw foods, as they are probably done on people that have never tried raw meat before, rather than on someone who’s been doing such a diet for at least a year.
    That said I’ve never been able to adapt to completely raw diet, it always leads to losing too much weight in the beginning and for someone that’s already thin it’s a disaster. Some people have stronger digestion/immune system and are able to adapt quickly.

    • diana

      Cooked food is optimal.

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    • diana

      I do not recommend eating raw spinach as it contains lots of oxalic acid, which can inhibit calcium absorption though binding to minerals in intestinal lumen.

  • http://www.facebook.com/medicinus Leonardo Gonzalez

    I’m going to keep juicing Kale — it seems glucosinolates do more good than bad, especially if you’re not suffering from hypothyroidism:

  • Diana Paez

    support your claims please.

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  • Faye Brown

    Well this explains why every time I ate a bowl of Kale which I had bought for the first time … it ran my blood pressure up sky-high … and I eventually threw the rest of what I had cooked away

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  • Engelhafen .

    You’re mixing a lot of things here – most importantly there are many ways to eat raw. I emulsify most of my food for the past few yeas and I’m a weight lifter and in super great shape. I’ve never felt better in my life and have had no illnesses in those years and my allergies have been so reduced that I no longer take ANY allergy medications for the first time in over 50 years! I emulsify collards, kale, beets, carrots and as many veggies as I can. Emulsification breaks down cell walls and makes it very ears to digest these foods – for me. Let’s remember that fire did not enter the equation in humanity until quite late in our evolution. Our bodies are still very much in that time-era.