Does raw food contain more nutrition than cooked food?
Let us have a look at the evidence shall we…..
Certain vitamins are known to be affected by forces such as water, light, air and heat. More specifically the following table provides an overview of what element affects which vitamin (1) –
Overall vitamins lost during cooking is not large and can range from 10-25%. This of course depends on the cooking temperatures and times, where the higher the degrees and the longer time will cause greater losses of vitamins (2). Large variations in nutritional value can be found in any type of fruit or vegetable depending on how and where it was grown, when it was picked in its maturing cycle and how long it has been sitting around. Considering how varied these levels can be anyway, the amount which might be lost in cooking is probably not as important as the quality of the produce in the first place.
On the other hand, cooking food can actually increase the availability of some nutrients too. For example, starchy foods such as potatoes, grains and legumes are much more easily digested, while lycopene in tomatoes become more easily absorbed once cooked. A number of carotenoids such as beta-carotene in orange and green vegetables also become more bioavailable once they are heated, however over cooking has the opposite effect (3). Heat also improves the solubility of some of the beneficial compounds in various spices such as turmeric (4).
When we consider minerals, heating as such does not affect these but they may be leeched out into water while being boiled. This is similar to the vitamins we looked at above that are affected by water, which is the reason steaming vegetables is better to boiling them in water! If you are going to boil vegetables like in soups or casseroles, the minerals will stay in the sauce.
Other food processes which affect the nutrient content of food can include milling, canning and freezing. Milling is the refining process which turns whole grains into their white counter parts. This process pretty much removes any of the vitamins and minerals of the grain leaving behind only the carbohydrate and protein portion. Frozen and canned foods are generally blanched prior to packaging so can affect vitamin C and some of the B vitamins. Canning involves a further high temperatures process so nutritional losses of these vitamins is greater (5).
There are a number of other food components that can affect the digestion and absorption of many of our nutrients (6), but this is going a bit beyond the scope of this article and will be covered in more detail in the final session of the Vitality Time Wellness Programme Series.
I will leave you with one last thought about how traditional cultures see the process of digestion. In both Ayurveda and Traditional Chinese Medicine, it is thought that digestion is a heating process and this fire is needed to extract out the vital nutrients. It is written that consuming too many cold or raw foods can put out this fire………food for thought?
In essence given the information above, it seems sensible to be trying to get a good balance of both and as always any vegetables is better than no vegetables!!
1. Gropper, SS and Smith, JL. 2013. Advanced Nutrition and Human Metabolism 6th Ed. Wadsworth/Cengage Learning. Belmont, CA.
2. Asadullah et al. 2010. Study to evaluate the impact of heat treatment on water soluble vitamins in milk. Journal of Pakistan Medical Association 60:11; 909-912.
3. Maiani, G. et al. 2009. Carotenoids: actual knowledge on food sources, intakes, stability and bioavailability and their protective role in humans. Molecular Nutrition Food Research 53 (Suppl 2): S194-218.
4. Kurien, BT. et al. 2007. Improving the solubility and pharmacological efficacy of curcumin by heat treatment. Assays in Drug Development Technology 5:4; 567-576.
5. Lupien, JR., Lin, DX. 2004. Contemporary food technology and its impact on cuisine. Asia Pacific Journal of Clinical Nutrition 13:2; 156-161.
6. Gibson, RS. 2007. The role of diet- and host-related factors in nutrient bioavailability and thus in nutrient-based dietary requirement estimates. Food and Nutrition Bulletin 28: (1 Suppl Int); S77-100.