Nutrition Myth #3 - Carbs are Carbs

We are often told carbs are bad for us, or to avoid carbs. Why?

Refined carbs are also known as simple carbs, processed carbs or white carbs.  There are three main types:

  • Sugars: Refined and processed sugars, such as sucrose (table sugar), high fructose corn syrup and agave syrup, natural sugars in fruit and honey, added sugars in processed foods, and alcohol.

  • Refined grains: These are grains that have had the fibrous and nutritious parts removed. The biggest source is white flour made from refined wheat.  Refined carbs have been stripped of almost all fibre, vitamins and minerals.  For this reason, they can be considered as “empty” calories.

  • Starches:  Starchy vegetables such as potatoes are nutrient-free carb grenades – 60%-80% starch.  Starch starts breaking down in your mouth.  As you chew, more saliva is secreted.  Saliva clings to starch and begins deconstructing these large, branched compounds.  Starch converts into maltose, a smaller, simpler carbohydrate, right in your mouth.  Maltose heads down to your small intestine, where it converts to glucose and is free to enter your bloodstream.

The main dietary sources of refined carbs are white flour, white bread, white rice, pastries, soft drinks, alcohol, snacks, pasta, sweets, breakfast cereals and anything with added sugars.  White carbs are also digested quickly and have a high glycemic index (GI); they lead to rapid spikes in blood sugar and insulin levels after meals.

These are the carbs we should avoid or reduce our intake of.

The Glycaemic Index

Some foods traditionally thought of as complex carbohydrates, such as wholegrain bread (GI 52), have a lower glycemic index than simple carbohydrates, such as glucose (GI 100).  The GI for other complex carbohydrates, such as potato (GI 80-90), are actually higher than sucrose (refined white sugar (GI 65)) and some conventionally complex carbs such as white bread and supposedly ‘healthy’ muesli or granola (GI 65) have a similar GI to pure sugar.

 

Whole Grains

Whole grains are very high in dietary fibre (1) and consist of three main parts (2, 3):

  • Bran: The hard outer layer, containing fibre, minerals and antioxidants.

  • Germ: The nutrient-rich core, containing carbs, fat, protein, vitamins, minerals, antioxidants and plant compounds.

  • Endosperm: The middle layer, containing mostly carbs and small amounts of protein.

 

The bran and germ are the most nutritious parts of whole grains, containing high amounts of many nutrients, such as fibre, B vitamins, iron, magnesium, phosphorus, manganese and selenium.  During the refining process, the bran and germ are removed, along with all the nutrients they contain (4) leaving only rapidly digested starch with small amounts of protein.

These high GI foods promote short-term fullness, lasting about one hour compared to low GI foods which promote a sustained feeling of fullness, lasting about two to three hours (5, 6).

The reduction in blood sugar promotes hunger and stimulates parts of the brain associated with reward and craving (7, 8).  Long-term studies have also shown that eating refined carbs is linked with increased belly fat over the course of just five years (9, 10).

Consuming a high amount of refined carbohydrates can have numerous adverse health effects. However, not all carbs are bad.  Some carbohydrate-rich, whole foods - including vegetables, fruit, legumes, root vegetables and whole grains, such as oats and barley - are extremely healthy, if not necessary -  as great sources of fibre, vitamins, minerals and various beneficial plant compounds.

Unless you are following a carb-restricted diet, there is absolutely NO reason to avoid these foods just because they contain carbs.  These carbs will leave you fuller, for longer and ween you off the white carb craving.

References

  1. Thompson FE, Sowers MF, Frongillo EA Jr, Parpia BJ.  (1992)  “Sources of fiber and fat in diets of US women aged 19 to 50: implications for nutrition education and policy.  American Journal of Public Health.  May;82(5):695-702.

  2. Slavin J.  (2003)  “Why whole grains are protective: biological mechanisms”.  Proceedings of the Nutrition Society.  Feb;62(1):129-34.

  3. Slavin JL, Martini MC, Jacobs DR Jr, Marquart L.  (1999)  “Plausible mechanisms for the protectiveness of whole grains”.  American Journal of Clinical Nutrition.  Sep;70(3 Suppl):459S-463S.

  4. Steffen LM, Jacobs DR Jr, Stevens J, Shahar E, Carithers T, Folsom AR.  (2003)  “Associations of whole-grain, refined-grain, and fruit and vegetable consumption with risks of all-cause mortality and incident coronary artery disease and ischemic stroke: the Atherosclerosis Risk in Communities (ARIC) Study”. American Journal of Clinical Nutrition.  Sep;78(3):383-90.

  5. Roberts SB.  (2003)  “Glycemic index and satiety”.  Nutrition in Clinical Care.  Jan-Apr;6(1):20-6.

  6. Anderson GH, Woodend D.  (2003)  “Effect of glycemic carbohydrates on short-term satiety and food intake”. Nutrition Reviews.  May;61(5 Pt 2):S17-26.

  7. Lennerz BS, Alsop DC, Holsen LM, Stern E, Rojas R, Ebbeling CB, Goldstein JM, Ludwig DS.  (2013)  “Effects of dietary glycemic index on brain regions related to reward and craving in men”.  American Journal of Clinical Nutrition.  Sep;98(3):641-7

  8. Ludwig DS, Majzoub JA, Al-Zahrani A, Dallal GE, Blanco I, Roberts SB.  (1999)  “High glycemic index foods, overeating, and obesity”.  Pediatrics.  Mar;103(3):E26.

  9. Halkjaer J, Tjønneland A, Thomsen BL, Overvad K, Sørensen TI.  (2006)  “Intake of macronutrients as predictors of 5-y changes in waist circumference”.  American Journal of Clinical Nutrition.  Oct;84(4):789-97.

  10. Halkjaer J, Tjønneland A, Overvad K, Sørensen TI.  (2009)  “Dietary predictors of 5-year changes in waist circumference”.  Journal of the American Dietetic Association.  Aug;109(8):1356-66