Nutrients From Food: Are We Getting What We Pay For?

A recent survey of diet and nutrition in the UK has found that many people show deficient dietary intake of some of the most important vitamins[1]. Out of over 1,500 adults tested, 14% of men and 15% of women where deficient in vitamin D, 6% of men and 19% of women were deficient in potassium and 9% of men and 13% women were deficient in magnesium. The easiest way to increase nutrient intake is to consume more nutrient rich foods such as nuts, seeds, fruits and vegetables and whole grains; indeed, only 1/3 people in the UK consume at least 5 fruit/veg a day[2]. This suggests that upping our consumption of nutrient dense foods will address the nutrient deficit. But is that the end of the story?

Some research suggests that the amount of a particular nutrient or vitamin that is present in a food is not necessarily related to how much of that nutrient is used by our bodies[3]. ‘Bioavailability’ refers to the proportion of a nutrient that is available to the body after we eat a food item. Some food items display a good match between the amount of potential nutrients available and the availability of those nutrients once they enter the body (e.g. black tea); others however, can have up to a 100% reduction in the amount of potential nutrients available after we eat them. This means that although there may be a high amount of nutrients present in a food item before we eat it, these nutrients may not be effectively digested and used by the body.

There are a number of factors which may affect the bioavailability of nutrients during digestion. These include the chemical form of the nutrient, the structure and amount of other foods present in the digestive system, metabolism and the amount of time taken for the food to move through the intestine. Food processing such as grinding, fermentation and/or mild heating may improve bioavailability; these processes disrupt cell walls which increases uptake of nutrients in the gut. For example, one piece of research finds bioavailability of nutrients from carrot juice is 70% higher than availability from raw carrots[4]. Further research found that daily consumption of processed carrots over a period of 4-weeks increased the amount of beta-caratone (source of vitamin A) in the blood three times as much as the consumption of the same amount of raw carrots.

So, undergoing processing may affect the availability of the nutrients from food. However, the type of processing may also have an effect. For example, there is a decrease in flavanols (antioxidants) during fermentation and drying of cocoa beans but not during roasting. There also might be an effect of individual differences in the gut microbiota (the microbe population living in our intestine). While each of us has a unique microbiota, it always fulfils the same physiological functions; helping the body to digest certain foods and participating in immune system function. However, not all gut microbiomes have equal abilities. For example, the ability of the gut to digest certain compounds from algae-based foods (e.g. seaweed) is much greater in Japanese people than in Americans[5]. This is likely to be due to interactions between food customs, dietary history and gut microbiome composition.

It is this information which has caused some researchers to comment on the accuracy of daily guidelines for nutrient intake. Extreme deficiency in one or more nutrients can cause serious health problems. However, it is not necessarily the lack of consumption of food rich in particular nutrients which might cause such a deficiency; there are many other factors which are involved in nutrient absorption. It is therefore important to eat a varied diet which is high in nutrient rich foods that have been processed in a variety of ways (raw, fermented, heated, liquified, boiled etc.) in order to maintain a healthy balance of nutrients within the body.

_____________________________________________________________________________________________________

[1] http://www.stewartnutrition.co.uk/nutritional_assesment/national_diet_and_nutrition_survey_19-64.html

[2] http://www.dailymail.co.uk/news/article-3839227/UK-best-Europe-eating-five-day.html

[3] Parada, J., & Aguilera, J. M. (2007). Food microstructure affects the bioavailability of several nutrients. Journal of food science, 72(2), R21-R32.

[4] Parada, J., & Aguilera, J. M. (2007). Food microstructure affects the bioavailability of several nutrients. Journal of food science, 72(2), R21-R32.

[5] Wells, M. L., Potin, P., Craigie, J. S., Raven, J. A., Merchant, S. S., Helliwell, K. E., … & Brawley, S. H. (2016). Algae as nutritional and functional food sources: revisiting our understanding. Journal of Applied Phycology, 1-34.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s