Science on Sunday: Glycemic Index

One of the problems with science is how it is reported in magazines and newspapers.  Also how it is reported on the web can be a problem.  This problem came to light for me when I was reading the free magazine “Better Nutrition”.  In the February issue there was a short article on “The best weight management diet” which talked about a New England Journal of Medicine article which showed that high protein-low glycemic index diets were better for maintaining weight loss.  This sound realistic and was confirmed by reading the article, but what peeked my interest was the table of glycemic index values in the Better Nutrition article because apparently sourdough bread has a lower GI (54) than white bread (100).

This did not seem possible as sourdough bread is essentially made from the same ingredients as white bread with a different starter is added instead of yeast for proofing.  There is nothing in the process of making sourdough bread that should change the carbohydrates, which are from wheat flour.

So I looked up how glycemic index was measured.  What I found was that glycemic index (GI) ranks foods by how quickly they increase blood sugar (glucose) levels.  Foods that increase blood sugar rapidly after being consumed have a high GI.  For example, honey has a GI of 85 and sucrose, table sugar, has a GI of 70. Conversely foods which are slowly digested and absorbed have a low GI.    Examples of these foods are green vegetables (GI = 15) and dark chocolate with greater than 70 % cocoa solids (GI = 22).

GI is measured by feeding measured portions of the test food containing 10 – 50 grams of carbohydrate to 10 healthy people after an overnight fast.  Blood samples are taken at 15-30 minute intervals over the next two hours and used to construct a blood sugar response curve. The area under the curve (AUC) is calculated to reflect the total rise in blood glucose levels after eating the test food.  The results for a test food is divided by the results of the standard containing the same amount of carbohydrate, either glucose or white bread are used as standards, and multiplied by 100.  The result gives a relative ranking for each tested food.  There is some concern, firstly that the standards used are different and secondly two hours after a meal is too short.  Food is known to stay in the stomach for over 4 hours, so longer term blood glucose monitoring might be better.

The glycemic index was developed at the University of Sydney (Australia) originally to aid people with diabetes control their blood sugar levels.  Low GI diets are useful for people with diabetes as it allows them to regulate their blood sugar levels and this in turn helps with insulin levels and may reduce insulin resistance for people with Type II diabetes.

So the more I read, the less likely it seemed that sourdough bread could have a lower glycemic index than white bread, which by the way, in some measurements of GI is set as the reference with a GI of 100 and in others, where glucose is the reference, white bread has a GI of 70.  Yes, not even the measurements of GI are standardized.

Interestingly it seems that the reason the high protein/low glycemic index diets work is that protein fills you up and after eating a meal that is high in protein you are more satisfied.


Thomas Meinert Larsen, et al, Diets with High or Low Protein Content and Glycemic Index for Weight-Loss Maintenance N Engl J Med 2010; 363:2102-2113 doi:10.1056/NEJMoa1007137


Tasty Tuesday: Food Rules

Michael Pollan has a new book which gives the rules (guidelines) towards health eating.  My copy is on its way from Amazon and I’ll let you know what I think when I’ve read it.  In the meantime here is an interview from the Daily Show,  links to an article in the YT, to an interview at SlashFood and to an excerpt of the book at ABCnews.

(Hat-tip: Thanks to colleagues RG and RR for the original link.)

BTW, Tropicana Trop50 is disgusting, unfortunately proving Michael Pollan’s point about food manufacturing.  Once my current carton is gone, I’m sticking to straight orange juice.  If I want less sugar, I’ll dilute it.

Book Review Part 2: In Defense of Food. Part 1: The Age of Nutritionism

Review: Part 1

In Defense of Food by Michael Pollan, January, 2008, Penguin Press, p 244, US$21.95, ISBN: 978-1-59520-145-5


English Cover Image

As mentioned in the first part of my review of “In Defense of Food”, nutritionism is not same as nutrition, which is a science, but it is the ideology surrounding food as only a supply of nutrients. The term was defined by Gyorgy Scrinis in 2002:

“[…] namely, that we should understand and engage with food and our bodies in terms of their nutritional and chemical constituents and requirements – the assumption being that is all we need to understand.”

Foods are used to promote physical health with some nutrients being “good” and others being “bad”. In the nineteenth century the German organic chemist Justus von Liebig promoted meat as it was high in protein. For any British readers, Von Liebig meat extract company developed OXO. Protein was the master nutrient as eating more protein lead to bigger and, obviously, healthier people. However, for every “good” nutrient we need a corresponding “bad” nutrient, hence leading to fads of anti-fat, anti- carbohydrate, or anti-protein.

The biggest problem with nutritionism is that it is only based on nutrients that can be measured. At first this meant the macronutrients protein, fat and carbohydrates. As analytical technology improves, there is more concern about food components, both good and badthat are present in smaller and smaller amounts. This explains the recent interest in phytochemicals and in potential carcinogens such as heterocyclic amines and acrylamide.

The increase awareness of food as a supply of nutrients lead to the development of dietary guidelines and this, in turn, lead to the golden age for food science [technology]. I do agree that it is ridiculous that processed food items, such as Cheerios, can have a health claim while fresh produce, such as carrots, do not. As Pollan’s biggest criticism of science is that food animals are now breed to be leaner; ignoring that fact that before the 1980s, beef and pigs were originally breed to be fatter, I do contest that he is being selective with the science being used.

For example, Pollan quotes extensively from an article by Frank et al (2001)* but with this quote I have doubts about their nutritional knowledge:

“Surprisingly, there was little direct evidence linking high egg consumption and increased risk of CHD – surprisingly [Pollan goes on to write], because eggs are particularly high in cholesterol.”

This should not be surprising to any nutritionist. I was taught in the 1980s that dietary cholesterol has NO bearing on serum cholesterol levels unless you suffer from some form of hyperlipidaemia. Thus, dietary cholesterol is less of a risk than dietary fat.

Additionally, there is a problem with Pollan’s critique of dietary guidelines and the food industry, some of which I addressed earlier. Pollan is justifiably very critical about trans fats as they appear to have turned out to be more harmful that traditional saturated fats, but like Taubes, he is selective in the scientific literature he uses to discuss the low-fat diet. The biggest criticism I have of Pollan and Taubes is that they IGNORE both calories and physical activity. This may be a fault of the dietary guidelines; until the latest version of the food pyramid, exercise was not mentioned in relationship to diet. Additionally, Pollan ignores the increase in portion size and that effect on diet. Ask any European visiting the US for the first time – portions here are huge, but my experience tells me that you soon adapt to this and start feeding yourself more at home too.

The biggest problem, in my opinion, with the low-fat dietary theory is that people are now scared of fat and think they should not eat any. They eat low fat everything without considering the taste. It would be better to eat smaller amounts of high fat food than a large portion.

According to Pollan the biggest problem with nutrition is that it is, like most sciences, a reductionist science. Understanding how our body responds to food and nutrients is enormously complex. Most nutrition studies isolate one part of the diet; whole grains or fiber, for example; and study its effect on one bodily function; for example, weight or serum cholesterol; without considering either the whole diet or the whole body. However, changing your intake of whole grains may alter your intake of fruit and vegetables.

I do agree with Pollan’s conclusion:

“Now, all this might be tolerable if eating by the light of Nutritionism made us, if not happier, then at least healthier. That is has failed to do. Thirty years of nutritional advice have left us fatter, sicker, and more poorly nourished. Which is why we find ourselves in the predicament we do: In need of a whole new way to think about eating.”

Part three of my review, Part II: The Western Diet and Diseases of Civilization, to follow.

Frank et al (2001) Types of Dietary Fat and Risk of Coronary Heart Disease: A Critical Review. Journal of the American College of Nutrition. 20(1) 5.

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Berries and Cancer

Dig those blackberries from last summer. Any excuse to reuse my photos! We all know we should be stuffing our faces with lots of fruits and veggies, but what is the evidence and which ones are the best?

In a recent article (1), Seeram reviewed the evidence that berries prevent cancer. This review was a little frustrating to follow, and I started wondering if it was a rewritten introduction to a grant application. For an article published in the Journal of Ag. and Food Chem., I personally could have done with a better overview. Some of the detail, while may be necessary in a cancer journal, lost me without careful concentration and then I lost myself in the acronyms. You may realize this from the discussion below. To be fair, they did explain quite a bit of the science and the subject knowledge might be all over the place with different researchers studying different berries and cancers.

In the USA, commonly consumed berries include blackberries, black and red raspberries, blueberries, cranberries, and strawberries. The active ingredients in berries includes Vitamins A, C, E and folic acid; calcuim and selenium; phytosterols; and phenolic molecules such as anthocyanins, flavonols and tannins.

So how good are berries at preventing and reversing cancer?

In vitro studies, with cell lines, have shown that berry phenolics in addition to being potent antioxidants, they also:

“[…]exhibit anti-inflammatory properties, are able to induce carcinogen detoxification (phase-II) enzymes, and modulate subcellular signaling pathways of cancer proliferation, apoptosis and tumor angiogenesis […].”

Coo. That sounds good, but as I am not a cancer researcher the details of the reviewed studies were difficult for me to follow. Raspberry, cranberry and lowbush blueberry juices showed the strongest inhibition of cell growth, which is good as we do not want cancer cells to grow. A red raspberry extract treated so it went through conditions that mimicked the digestive system decreased the number of colon cancer cells and protected against DNA damage induced by hydrogen peroxide. Blueberries induced apoptosis (cell death) of cancer cells and may influence prostate cancer cells [I assumed to the good]. Cranberry extracts inhibited the growth of human breast cancer.

Animal studies showed that rats fed berries and fruit juices showed a significant reduction in AOM-induced aberrant crypt foci, which is a leading indicator of colon cancer. AOM is azoxymethane and acts as a carcinogen to trigger colon cancer in rats and mice.

As for human studies:

Increased fruit and vegetable consumption has been associated with the decreased risk of a number of cancers of epithelial origin, including esophageal cancer.

As an aside, I prefer the British spelling for oesophagus, the oe looks more dignified and I do say “oh-sophagus” or “oo-sophagus”

It is hard to know how much bioactives we are consuming. This is partly, as this article reports, because the amount of phytochemicals present in foods is not known and changes dramatically depending on growing conditions. Organic strawberries had a greater effect on human colon and breast tumor cells than conventionally grown strawberries. Organic berries were more effective probably because they contain more secondary metabolites than conventionally grown fruit.In addition:

Studies have shown a high variability in phenolic intake based on variations in individual food preferences. A high daily intake of fruits and vegetables is estimated to provide up to 1 g of phenolics.

Unfortunately, “high daily intake of fruits and vegetables” is not defined in the article.

Even if we know how much of the bioactive compounds we consume, we still do not know how bio-available these phenolics in berries or other fruit.

I find it amusing that articles always end up with a statement which in effect says “more research is needed, I am the best person to do it and I need funding now“. In this article the concluding paragraph goes:

In conclusion, it is strongly recommended that this area of research for berry fruits continue to be explored, as this will lay the foundation for the development of diet-based strategies for the prevention and therapy of self types of human cancers.

My conclusion?

Eat lots of berries, now and forever more. Fortunately, I have lots in my freezer. Yum.


(1) Seeram, N.P. (2008). Berry Fruits for Cancer Prevention: Current Status and Future Prospects. Journal of Agricultural and Food Chemistry DOI: 10.1021/jf072504n