The short answer is - yes. If you consistently eat a diet filled with a wide variety of fruits, vegetables and whole grains, you may be able to get all of the macronutrients and micronutrients you need to stay healthy. However, life is often more complex than short answers can encapsulate. The problem is most people do not eat this way and therefore it’s unlikely that this is the case. The fact is, is that our lifestyle often precludes us from getting the nutrients we need. Whether it’s ordering out, or grabbing snacks to quell our hunger, it’s feasible to deduce that many times we are simply grabbing the easiest most delicious thing to eat, which often include a lot of carbohydrates and lipids that aren't always conducive to our wellness.

The more nuanced longer answer to this question is - yes you can rely on food-based absorption of nutrients, but you probably are not eating right to actually get the nutrients you need. The small intestine and the rest of the digestive tract can only do so much to absorb the nutrients we need, but no number of enzymes or probiotics in our gut microbiome can absorb nutrients that aren't there to start with. This is the case for a variety of reasons that go beyond our own individual choices regarding what we consume. How we consume food also has a profound effect on nutrient absorption. Many people believe that eating raw vegetables versus cooked ones is preferable because we might think intuitively raw vegetables should maintain their nutritional content more. However, this all depends on the type of nutrient consumed. Calcium absorption will work differently than glucose, which is even different from the similar fructose, which are all massively different from fatty acids and even healthy fats. Even water-soluble vitamins and fat-soluble vitamins of the same type have very different journeys through the digestive system. 

One study of 200 people in Germany found those who ate a raw food diet found that they had higher levels of beta carotene, but their plasma lycopene levels were well below average. That’s likely because fresh, uncooked tomatoes actually have lower lycopene content than cooked or processed tomatoes. Cooking breaks down the thick cell walls of many plants, releasing the nutrients stored in them.

In another study it was shown that fat-soluble compounds like vitamins A, D, E and K and the antioxidant compounds called carotenoids fare better during cooking and processing. This doesn't necessarily mean malabsorption without heat, it just signals that the gastrointestinal tract may respond to the availability of these nutrients differently depending on their cooking method. A report in the Journal of Agricultural and Food Chemistry concluded that over all, boiling was better for carrots, zucchini and broccoli than steaming, frying or serving them raw. Frying vegetables was by far the worst method for preserving nutrients. broccoli than steaming, frying or serving them raw. Frying vegetables was by far the worst method for preserving nutrients.

As you can see, the nutritional absorption landscape is complicated by a myriad of factors. This confusion has led to an explosion in the amount vitamin supplement companies offering “solutions in a pill” to make up for our nutritional deficiencies, especially focusing on magnesium, vitamin B12, amino acids, potassium, and electrolytes, and most of the time, without even making sure that the form of the vitamin included in the supplement is in a processable and bioavailable form absorbable by our intestinal metabolic processes. The industry has been rife with empty marketing promises due to its highly unregulated nature. Therefore, any cursory research online will turn up plenty of negative articles about the ineffectiveness of supplements. The majority of this criticism is fair as many of these vitamin companies aren’t particularly interested in science as much as they are in moving products. However, we have a fair amount of evidence to suggest that when vitamins are dosed correctly with high quality ingredients, they can be extremely beneficial. One prominent example is pregnant women are often told by their doctors to take 400 micrograms of folic acid daily to prevent spina bifida in newborns. Additionally, many people, especially those living in colder northern climates are often told to take Vitamin D supplements to help fortify their immune system. Those suffering from anemia or having strict vegetarian diets are often told to take iron supplements as their diets may be lacking this essential nutrient. Anyone who has dosed themselves with vitamin C can attest to its power to shorten the length of their illness.

In conclusion, food is best for nutrient absorption but due to food supply and varying cooking methods, along with our own choices, we are probably not getting enough of what we need on a daily basis. While just taking any supplement may not be the answer, taking the right one(s) backed by science can make a world of difference.

Sources:

Garcia AL, Koebnick C, Dagnelie PC, Strassner C, Elmadfa I, Katz N, Leitzmann C, Hoffmann I. Long-term strict raw food diet is associated with favourable plasma beta-carotene and low plasma lycopene concentrations in Germans. Br J Nutr. 2008 Jun;99(6):1293-300. doi: 10.1017/S0007114507868486. Epub 2007 Nov 21. PMID: 18028575.v

Cristiana Miglio, Emma Chiavaro, Attilio Visconti, Vincenzo Fogliano, and Nicoletta Pellegrini

Journal of Agricultural and Food Chemistry 2008 56 (1), 139-147

DOI: 10.1021/jf072304b