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Eating raw foods seem to hold a place of great esteem in the popular nutrition world, being held up high as the best, “most natural” way to get our nutrients from food. On the surface, this may seem like a perfectly logical conclusion; raw fruits and vegetables are unadulterated by heat, and thus the nutrients, supposedly, remain intact.
But, is it really that simple?
It isn’t. Today, you are going to learn why.
There is scientific evidence that shows that raw fruits and vegetables are not always the best option when it comes to getting the most nutritional bang for your buck. Sometimes, cooked plants are actually better for your health. It all depends on 1) what nutrients you are looking at, and 2) what health problems you may be dealing with.
Here is an outline of what is to come in this article:
Topic 1: Cooking and human evolution
Topic 2: When cooked is better than raw
Topic 3: When raw is better than cooked
Topic 4: Research on the benefits of both combined
Topic 5: Health conditions for which cooked is better
Topic 1: Cooking and human evolution
Let’s start with a little background on cooking. Simply put, the cooking process breaks down the food matrix to make nutrients more accessible – which is a good thing – but the heat can also cause thermal degradation of nutrients, which means that the nutrients get damaged and broken down, and we get less of them overall from our food.
Despite its potential drawbacks, cooking is believed to have played a critical role in our evolution as humans. This is because cooking externalizes part of the digestive process, which in turn increases the amount of energy that we obtain from food. Applying heat to your food before eating it also kills off lots of the bacteria that would otherwise make you sick. Lastly, cooking also improves the palatability and flavor of many foods.
It has been argued that knowing how to handle pots and pans is what made us more intelligent than our evolutionary kin.
Research shows that people who attempt to follow a fully raw food diet report being persistently hungry. It seems that our species really has adapted to eating cooked food, and the small size of our molars and total gut volume support this notion. Cooked foods are often nutritionally superior to raw foods; we will cover some examples of foods that exemplify this truth next.
Topic 2: When cooked is better than raw
Example 1: Tomatoes
The first example of a plant food that is more nutritious when cooked is tomatoes. The lycopene in tomatoes, which is a potent antioxidant that has been shown to reduce prostate cancer risk and protect against heart disease, is much easier for our bodies to absorb from cooked tomatoes.
This is a big deal because prostate cancer is the second leading cause of death due to cancer in men in the United States. 1 in 8 men will receive a diagnosis of prostate cancer at some point in their lives, and 1 in 41 will die from it.
The research evidence connecting lycopene to reduced prostate cancer risk is pretty strong. In this meta-analysis, 26 studies with over 17,000 cases of prostate cancer and over half a million participants altogether were analyzed. Researchers concluded that there was a trend of lower prostate cancer incidence with higher lycopene intake.
This conclusion is bolstered by the observed dose-response relationship, and the positive association between higher circulating levels of lycopene in the blood and a reduced risk of prostate cancer. This means that the more lycopene men consumed, the more they had in their blood, and the more protection they had against prostate cancer.
To get these benefits, you would need to consume 9-21 mg of lycopene per day, which you can get from just ½ cup of marinara sauce.
This simple sauce adds flavor AND reduces cancer risk, what more could we ask for?
Example 2: Vitamin E
Next, let's look at alpha-tocopherol, the primary form of vitamin E. If you are wondering what I mean by "primary form," don't worry, I'll explain. Vitamin E is actually an umbrella term for 8 different compounds - alpha-tocopherol is the one that is most active and hence, the most common topic for research on Vitamin E. For simplicity, I will just refer to alpha-tocopherol as vitamin E. This nutrient functions as an antioxidant, an immune system fortifier, and it keeps blood from clotting.
A Vitamin E family photo (Source: Fukui 2019).
In this study, researchers looked at the vitamin E content of numerous vegetables in their cooked and raw forms, and they found that in multiple instances, the measured amount of vitamin E was higher in the cooked form. For example: tomato paste had 9.4x the amount of raw tomatoes, cooked spinach had 2x as much as raw spinach, and boiled broccoli had 1.4x the amount of raw broccoli.
You can DOUBLE the vitamin E that you get from this spinach just by adding some heat to it. This comes at a cost though - more on that below.
Example 3: Antioxidants
To close this section on the benefits of cooking plant foods, I will cover the impact of cooking on antioxidants. I have heard people say that cooking kills off antioxidants, but that is not the full story at all! Before we get into the details, let’s talk a bit about what antioxidants even are.
Antioxidants help to protect our bodies against free radicals, which damage our body down to the DNA level and have been linked to diabetes, heart disease, cancer, rheumatoid arthritis, cataracts, and aging. Our bodies do produce antioxidants on their own, but increasing the amount of antioxidants circulating in your body by eating plant foods is highly beneficial.
Now, let's get more specific. Polyphenols are a class of antioxidants, and they come in many flavors. Think of polyphenols as an emergency kit – for your kit to be complete, you would need bandages, gauze, antibiotic ointment, alcohol, and so forth. Just the same, your body needs different types of polyphenols for effective protection. You need some that can remove free radicals, others that can activate antioxidant enzymes, others still that can chelate metal catalysts, ones that can inhibit oxidases, and so many more. If you haven't taken chemistry in a while, that last sentence may sound like complete gibberish. A straightforward way to look at it is that these are all descriptive terms of the different ways in which antioxidants keep our bodies in an optimal state. The next obvious question is, how can we extract as many antioxidants as possible from our food?
In this study on tropical green leafy vegetables, researchers found that most of the antioxidant compounds in these plants are easier for our bodies to absorb when the plant is cooked. This is because cooking breaks down the rough fiber of plants, which allows the polyphenols to be set free and become more accessible to our bodies. Some polyphenols increase in bioavailability (a measure of how easily our bodies absorb them) to an impressive degree after cooking. Take ferulic acid (found in corn, wheat, and oats) for instance, which increases up to 900% after 50 minutes of cooking. When we look beyond green leafy vegetables though, the data gets a bit more nuanced.
This study included other types of vegetables aside from leafy greens. They found that polyphenol content increased after cooking (boiling, steaming, or microwaving) for onion and potato, but went down for carrots, broccoli, and white cabbage. The free radical scavenging capacity - a measure of how well antioxidants can neutralize harmful substances in the body - of these vegetables was highest in broccoli after cooking. Carrots, onions, and white cabbage were more potent when raw.
In this study, cooking by various methods, including boiling, pressure cooking, baking, microwaving, griddling, and frying, generally led to reductions in the antioxidant capacity of some vegetables and enhancements for others. To summarize, boiling was fine for artichokes, eggplants, onions, beetroot, and asparagus, and not so good for pea, cauliflower, zucchini, spinach, broccoli, Brussels sprouts, carrot, leek, pepper and Swiss chard. For garlic and green beans, the findings were dependent on which antioxidant was being measured – lipoperoxyl radical scavengers, or hydroxyl radical scavengers.
I told you, this stuff is really nuanced. It will all make sense by the end though, I promise.
And the rest of the findings go on like that – each cooking method detonates antioxidants for some vegetables, maintains them in others, and boosts them in others still. The idea that cooking kills off all antioxidants is false, because there are so many types of antioxidants found in different foods, and they each respond differently in accordance with how the food is prepared. While it may not seem like it, vegetables are all unique chemical storehouses - this is a big part of why eating a variety of vegetables is so important.
You are ingesting a different blend of health boosting chemicals from every plant that you eat, so variety DOES matter.
Topic 3: When raw is better than cooked
If you have made it this far into the article, you may be convinced that cooking your veggies is generally the way to go. But, I will warn you that it is too early to make any conclusions just yet. Allow me to dazzle your mind with examples of when it is better to opt for plant foods in their raw form.
Example 1: Broccoli
Eating raw cruciferous vegetables like broccoli is linked to a reduced risk of bladder cancer.
Cruciferous vegetables like broccoli, cauliflower, Brussels sprouts, cabbage, and collard greens all have a pungent smell that comes from their sulfur-rich, cancer-fighting chemistry. The "bad" smell is actually a good thing.
Raw cruciferous vegetables generally contain higher amounts of isothiocyanates, which is a class of compounds that have been shown to keep cancer cells from multiplying and enhance the body’s natural detoxification system. Even if you can only manage to eat 1 serving of raw broccoli in a whole month, you would still get to enjoy a lower risk of bladder cancer than someone who avoids these vegetables altogether.
There is a way to get more health benefits from cooked broccoli though - you can sprinkle powered mustard seeds on them. Mustard seeds contain the same enzyme, myrosinase, that is needed to covert the dormant form of broccoli’s cancer-fighting sulfur compounds into their active form. Therefore, adding that enzyme to your broccoli can help boost the benefits you get from it even after it has been cooked.
Example 2: Water-soluble vitamins: Vitamin C and the B vitamins
Water-soluble vitamins are those that can be absorbed in water, e.g. vitamin C and the vitamins of the B complex. Some vitamins, like vitamin D, are more easily absorbed in fat. It tends to be the case that vitamins that absorb well in water also break down very easily when exposed to heat (see here, here, and here). This means that cooking foods rich in these vitamins, e.g. red and green peppers, broccoli, and cabbage, leads to very significant losses of these vitamins.
1 serving of sweet red pepper has more vitamin C than an orange - you can't taste it, but, it's there. Sadly, cooking destroys a significant portion of that vitamin.
Example 3: Mental health
There is some evidence that raw fruits and vegetables may be especially beneficial for mental health. This is a topic that needs to be studied more, but this study shows that eating up to 6 and a half servings of fresh plant matter each day was linked to less depression, a more positive mood, and more life satisfaction.
Beyond 6.5 servings of raw fruits and vegetables per day, the benefits drop off (Source: Brookie et al 2018).
Topic 4: Research on the benefits of both combined
Lastly, I want to cover research that highlights the value of eating both raw AND cooked fruits and vegetables. Both raw and cooked vegetables protect against cancer, which we know thanks to this paper. The most consistent protective effect was seen with cancers of the upper gastrointestinal tract. There was a tendency for the data to favor raw vegetables, but both types were beneficial.
Both raw and cooked vegetables also reduce risk for death from any cause. That was the key finding of this Australian research publication.
I’ve got one more outcome for you – coronary heart disease. In this 10-year study out of the Netherlands, it was found that both raw and cooked fruits and vegetables had similar benefits when it came to lowering one’s risk for coronary heart disease.
Topic 5: Health conditions for which cooked is better
Everything that I have discussed so far has been general information. However, as I mentioned in the introduction, certain health problems can impact what is actually best for a person.
Some health conditions require people to consume foods that are more easily digested in order to avoid irritation, inflammation, bloating, bleeding, and so forth. These include:
a. Inflammatory bowel syndrome,
b. Colon resection, and in some cases, even irritable bowel syndrome.
For most people though, the takeaway message should be this: it is best to try to have plant foods that are both raw and cooked, as both have their benefits. What matters most is that you are eating enough fruits and vegetables on a daily basis. For most people, that’s about 5 servings a day of fruits and vegetables.
Alright, take care!
References:
Topic 1: Cooking and human evolution
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Topic 2: When cooked is better than raw
American Cancer Society. (2022, January 12). Key Statistics for Prostate Cancer. Cancer.org; American Cancer Society. https://www.cancer.org/cancer/prostate-cancer/about/key-statistics.html
Chen P, Zhang W, Wang X, Zhao K, Negi DS, Zhuo L, Qi M, Wang X, Zhang X. Lycopene and Risk of Prostate Cancer: A Systematic Review and Meta-Analysis. Medicine (Baltimore). 2015 Aug;94(33):e1260. doi: 10.1097/MD.0000000000001260. PMID: 26287411; PMCID: PMC4616444.
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Fukui, Koji. (2019). Neuroprotective and Anti-Obesity Effects of Tocotrienols. Journal of Nutritional Science and Vitaminology. 65. S185-S187. 10.3177/jnsv.65.S185.
Jiyeon Chun, Junsoo Lee, Lin Ye, Jacob Exler, Ronald R. Eitenmiller. Tocopherol and tocotrienol contents of raw and processed fruits and vegetables in the United States diet,
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Dewanto V, Wu X, Liu RH. Processed sweet corn has higher antioxidant activity. J Agric Food Chem. 2002 Aug 14;50(17):4959-64. doi: 10.1021/jf0255937. PMID: 12166989.
A.L.K. Faller, E. Fialho. The antioxidant capacity and polyphenol content of organic and conventional retail vegetables after domestic cooking. Food Research International. Volume 42, Issue 1, 2009, Pages 210-215.
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Topic 3: When raw is better than cooked
Tang L, Zirpoli GR, Guru K, Moysich KB, Zhang Y, Ambrosone CB, McCann SE. Consumption of raw cruciferous vegetables is inversely associated with bladder cancer risk. Cancer Epidemiol Biomarkers Prev. 2008 Apr;17(4):938-44. doi: 10.1158/1055-9965.EPI-07-2502. PMID: 18398034.
Tang L, Zirpoli GR, Guru K, Moysich KB, Zhang Y, Ambrosone CB, McCann SE. Intake of cruciferous vegetables modifies bladder cancer survival. Cancer Epidemiol Biomarkers Prev. 2010 Jul;19(7):1806-11. doi: 10.1158/1055-9965.EPI-10-0008. Epub 2010 Jun 15. PMID: 20551305; PMCID: PMC2901397.
Ghawi SK, Methven L, Niranjan K. The potential to intensify sulforaphane formation in cooked broccoli (Brassica oleracea var. italica) using mustard seeds (Sinapis alba). Food Chem. 2013 Jun 1;138(2-3):1734-41. doi: 10.1016/j.foodchem.2012.10.119. Epub 2012 Nov 12. PMID: 23411305.
Brookie KL, Best GI, Conner TS. Intake of Raw Fruits and Vegetables Is Associated With Better Mental Health Than Intake of Processed Fruits and Vegetables. Front Psychol. 2018 Apr 10;9:487. doi: 10.3389/fpsyg.2018.00487. PMID: 29692750; PMCID: PMC5902672.
Rickman JC, Barrett DM, Bruhn CM. Nutritional comparison of fresh, frozen and canned fruits and vegetables. Part 1. Vitamins C and B and phenolic compounds. J Sci Food Agric. 2007 Mar 14;87:6(930-944). https://doi.org/10.1002/jsfa.2825
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National Institutes of Health. (2021, March 26). Office of Dietary Supplements - Vitamin C. Nih.gov. https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
Topic 4: Research on the benefits of both combined
Link LB, Potter JD. Raw versus cooked vegetables and cancer risk. Cancer Epidemiol Biomarkers Prev. 2004 Sep;13(9):1422-35. PMID: 15342442.
CDC. (2019). Head and Neck Cancers. Cdc.gov. https://www.cdc.gov/cancer/headneck/index.htm
Nguyen B, Bauman A, Gale J, Banks E, Kritharides L, Ding D. Fruit and vegetable consumption and all-cause mortality: evidence from a large Australian cohort study. Int J Behav Nutr Phys Act. 2016 Jan 25;13:9. doi: 10.1186/s12966-016-0334-5. PMID: 26810760; PMCID: PMC4727264.
Oude Griep LM, Geleijnse JM, Kromhout D, Ocké MC, Verschuren WM. Raw and processed fruit and vegetable consumption and 10-year coronary heart disease incidence in a population-based cohort study in the Netherlands. PLoS One. 2010 Oct 25;5(10):e13609. doi: 10.1371/journal.pone.0013609. PMID: 21049053; PMCID: PMC2963618.
5 a day recommendation:
Wang DD, Li Y, Bhupathiraju SN, Rosner BA, Sun Q, Giovannucci EL, Rimm EB, Manson JE, Willett WC, Stampfer MJ, Hu FB. Fruit and Vegetable Intake and Mortality: Results From 2 Prospective Cohort Studies of US Men and Women and a Meta-Analysis of 26 Cohort Studies. Circulation. 2021 Apr 27;143(17):1642-1654. doi: 10.1161/CIRCULATIONAHA.120.048996. Epub 2021 Mar 1. PMID: 33641343; PMCID: PMC8084888.
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