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.

Causes of Overweight

A commentary* by Gary Taubes in New Scientist puzzled me. He has forgotten the simple equation I was taught as a nutrition major:


If E is zero, your weight stays the same; if E is negative, you lose weight and if E is positive you gain weight. It really is that simple, but Mr Taubes says, in his introduction:

FOR the past century, the advice to the overweight and obese has remained remarkably consistent: consume fewer calories than you expend and you will lose weight. This prescription seems eminently reasonable. The only problem is that it doesn’t seem to work. Neither eating less nor moving more reverses the course of obesity in any but the rarest cases.

Mr Taubes argues that causality is the issue – what causes us to want to eat more. This, however, is still saying that we overeat. Even if hormones or a virus or addiction is responsible, if we consume more energy than expended we put on weight. We might not be to blame, but the truth is we are overweight because we took in more energy more than we burnt off.

It is not simple to lose weight. Losing weight requires a lot of effort and, most likely, an change in lifestyle. A change in what is usually quite a comfortable lifestyle. Losing weight is more than deciding not to eat a chocolate bar today. It requires the person to totally change how they approach food and exercise. They need to decide that they are going to change permanently, not just for the next month or so. Old influences will remain and keep on pushing you back to old habits. In fact, losing weight to keep the weight off, is not dissimilar from quitting smoking. The temptation to take up the old habits will always be there.

My story is that I never gained weight. I was one of the lucky ones with a fast metabolism. Then, after becoming a faculty member, I gained weight. I assume it was because I no longer spent long days walking around a lab. Instead I was sitting at the computer all day. I am more accustomed to American portion sizes, than I was in my first few years in the US. I also live in an area where it is more convenient to drive to the grocery (and other) stores – previously I would walk there or pass by on my bicycle on my way home. In other cities, I either had a significant walk (25 mins plus) each way or I cycled for the same length of time. I also was a keen walker (hiker in US terms) and would frequently spend Sunday in the hills around Yorkshire with friends. Somehow, I have not found an equivalent group of friends in my home town. As I have to make time to exercise, I do not do it often enough.

Perception of how much we eat and how we exercise is an issue that is frequently overlooked by writers including Mr Taubes. Thus, he ignores the fact that we perceive what we eat poorly; frequently eating more than we recall. I was glad to see, in the letters, that other NS readers had a similar reaction to Mr Taubes commentary. The first of these web letters states exactly the problem. Dieting does not work, because we do not keep to our diets.

In turns out, unfortunately, his commentary ends up being a plug for low carbohydrate diets. These diets were shown to be just as ineffective as low fat diets once there were enough food products available allowing us to return to our traditional way of eating, roughly three meals a day and snacks between. Initially, when the Atkins diet was first becoming popular, there was very little you could eat while following the diet correctly. Then, there were Atkins diet (or low carb) snack foods, which meant that we could eat in the traditional manner

He does make some interesting points that were made by Yudkin and others before:

… the consumption of refined carbohydrates, starches and sugars, all of which prompt (sooner or later) excessive insulin secretion. Insulin is the primary regulator of fat storage. When insulin levels are elevated, fat accumulates in our body tissue; when they fall, fat is released and we use it for fuel. By stimulating insulin secretion, carbohydrates make us fat; by driving us to accumulate fat, they increase hunger and decrease the energy we expend in metabolism and physical activity.

High sugar foods cause a “sugar rush” and then an opposite downturn in energy. A bit like taking drugs – you get the high, and unless you take more, you get the low. Even though this is a simplified view of the situation, but does imply that the constant consumption of sugary drinks would lead to insulin secretion being over extended.

Remember: If you want to lose weight, consume less calories than you use. You will need to be very honest about it and remove old temptations.


*Sorry, behind a pay wall:
Taubes, Gary 19 January 2008 “Comment: The great diet delusion”, New Scientist Print Edition.

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

Nutritional Properties of Beer

An interesting abstract just published online by the Journal of Food Science got me thinking. I have not read the whole article as I lack online access to JFS. The researchers at UCDavis:

[…] used surveys to compare beer and wine consumers’ perceptions of alcoholic and nonalcoholic beverages. The consumers ranked 7 beverages based upon perceived healthfulness both before and after they were exposed to nutritional information about the beverages.

While consumers perceived red wine to be the healthiest of seven beverages, the abstract does not answer the question as to whether beer and wine have any nutritional value.

We’ve all read the information that red wine contains compounds that reduce heart disease. This is meant to be part of the French paradox. In Britain, women just after child birth, were recommended to drink stout because it is rich in vitamins and minerals. However, as this Nutritional Facts panel shows, an American pint (16 fl oz) contains a whopping 196 calories.

Guinness Nutritional Facts

One of the problems is that alcohol is a source of calories. Whereas sugar and protein give 4 calories/g and fats give 9 calories/g, alcohol yields 7 calories/g. Unlike carbohydrates, protein and fat, which are used for maintenance and repair, alcohol only goes for energy production.

According to the USDA’s food composition tables, which only has “average” beer light beer or Budweiser, beer does not provide many minerals and it is helpful for B-vitamins especially niacin and folate. Red wine is slightly better providing some iron and a little B6, but 16 fl oz of wine, which I used to compare with beer, contains a whopping 1999 calories.

At least both are fat-free!

Dark beers, like dark chocolate, contain antioxidants, which make have beneficial health effects. These are formed, along with the color and flavor, by my favorite reaction: The Maillard reaction. Unfortunately, I cannot find any detailed nutritional facts for dark beers to prove if they are better nutritionally than lighter beers. Guinness has also been shown to prevent clots from forming. These clots increase the risk of heart disease.

So beer does not really add any nutrition to the diet – it sure tastes good though. Drinking one beer or one glass of wine per day has been shown be good for you. The drink helps you relax and may be sleep better at night. It is over drinking and binge drinking that are the problem.


C.A. Wright, C.M. Bruhn, H. Heymann, C.W. Bamforth. Beer and Wine Consumers’ Perceptions of the Nutritional Value of Alcoholic and Nonalcoholic Beverages,Journal of Food Science (OnlineEarly Articles).doi:10.1111/j.1750-3841.2007.00606.x

Guinness at Wikipedia

Magical (Properties of) Water – Part 1

Essentia Water Label


I bought this water at Whole Foods in Chapel Hill, which was conveniently in the same mall as the knitting store, Knit a Bit. I love wandering around places like Whole Foods to see what new and wonderful food I can buy. Their produce section is typically bigger than my house. It is very inspiring for a vegetarian food scientist.

I had to buy this water because of its ‘health’ claims. As I realise the above image is too small to read, I expanded each section and added commentary.


Front Detail

The ultimate drinking water, cor. I must drink a lot of this. Is it like Ultimate Frisbee? The water is purified enhanced using ionic separation. While they have nice diagrams of their purification method, it does not give details on their method of ionic separation. I assume it must be the same technique by which we obtain deionized water for the lab, which removes ions from water. Essentia then added electrolytes. Which are, aha, ions.


Nutrition Facts:

Essentia nutrition facts

Well, this water contains no nutrients. Not one. Nada. Unless you consider water to be a nutrient, of course.



Essentia ingredients

Electrolytes can’t be derived from sodium bicarbonate etc. as these are pure molecules. They are only derived from these molecules because in solution, any water based solution, the molecules become ionized producing Na+, HCO3 etc.

Electrolytes are important, Essentia’s website says so:

In a battery, the electrolyte fluid, creates an electrochemical pathway between one pole (+) and another (-). Electrolytes, minerals and salts do the same thing between your body’s cells in a network many billions of times more complex-and critical to maintaining normal blood pressure, restful sleep, proper cardiac rhythm, muscle strength, endocrine balance, intestinal function and more.

And more:

Essentia Water has been specifically formulated to rapidly restore intracellular fluids to their optimum state by taking advantage of the process the body naturally uses, the phenomenon of osmosis. Essentia Water has been designed to simulate intracellular fluid electrolyte concentrations. Solutions that have identical osmotic pressures are said to be isotonic solutions. For optimal and rapid replenishment of intracellular fluids and electrolytes, the replenishing fluid must be isotonic with intracellular fluids. [Their emphasis.]

So their you have it, electrolytes are a good thing. Actually, are they actually saying anything? After reading the first paragraph, I have this image of my cells having positive and negative poles with molecules lining up to the appropriate cathode or anode. I think not.

While Essentia don’t get into the details of ozonation, it is explained by the American Water Works [I must stop laughing. Waterworks is what my grandma called it when she need to pee or if I cried too much: “Switch off those waterworks, Lab Cat”] Association in this fact sheet. Unfortunately, this is the same method used by Coke to produce Dasani water in England. It caused bromate to form in the already pure and clean Thames tap water. Bromate is a potential carcinogen. Great, bottle free tap water, charge 95p per liter adding a carcinogen at no extra charge. Good thing none of those added electrolytes is bromide.

The statement about this water being bottled according the the requirements of the USEPA is a red herring. Bottled water is actually regulated by the FDA since it counts as a food. As this document shows, the EPA requires the FDA to adopt EPA’s water quality standards. This means that this water is a pure and clean as your faucet water. While searching for this information, I found this very informative document (pdf).

There is more…but that will have to wait for a second post. Too much information, not enough time.


Too Much Water

I mentioned in a previous post how much water we should drink but I don’t think I emphasized enough that you can have too much water. Now some one died after drinking too much water as part of a competition to win a Wii. It isn’t worth it! Orac has a couple of posts (1 & 2) and Radagast explains what goes wrong when you drink too much water.

It really is a stupid way to die!


I was trying to find a food science topic to write about. I have just gave my candy technology lecture to my freshman class and was going to write that up, and then realized that Exploratorium does a very good job of that already.


I then thought I should do something with a Thanksgiving theme, but with being British and vegetarian I don’t really celebrate a traditional Thanksgiving. I will be eating Vegetarian moussaka if any one is interested.

Which leads to flaxseed. One of my food chemistry class projects is on flaxseed because I published an article[1] on using flaxseed meal in whole-wheat muffins. The only major difference we found between muffins with and without flaxseed meal was that the batter with the flaxseed meal was significantly thicker. I actually did this project initially as a colleague who was studying the nutritional effects of flaxseed couldn’t do a double-blinded trial as at that time it was not clear as to how stable the nutritive components of flaxseed were. Also it is hard to discuss flaxseed in a food product such as muffin, as it adds a nutty flavor. Continue reading

Food Fables Nov 17 2006

One day I’ll have time to check these links out myself. Sigh.

Is a burrito a sandwich?

Will hemp seeds in bread make your kids happy?

Do mice like red wine?

Molecule of the Day: Saccharin

Cognitive Daily: Caffeine and concentration

Are red meat and breast cancer linked?

Draft Voluntary National Retail Food Regulatory Program Standards released by the FDA (hat tip IFT)

This week IFT also released Scientific Status Summaries on Organic Food and Food Nanotechnology.

FDA release two programs to help consumers understand the Nutrition Facts Panel: Make Your Calories Count interactive training program and a nutrition facts brochure (pdf). I’ll be using these in my freshman class next year!

Is there a problem with using corn to produce fuel rather than food? What about cost?

Janet reports on a ridiculous reaction to breast feeding. Sign the petition!

Don’t go to your doctor for nutritional advice

It was a joke when I was a nutrition undergrad (in England, graduated in 1987) that we had three years of intense human nutrition education and medical doctors were lucky to get eight hours. And yet who did people go to for dietary advice?

In 1985, the National Academy of Sciences found that an average of 21h of nutritional training was offered and that:

" Nutritional education programs in US medical schools are largely inadequate to meet the present and furture demands of the medical professions."

An article in NutraIngredients,USA suggests that things haven't improved much since. A recent survey of 106 American medical schools showed an average of 23.9h (see figure below) of nutritional education; most of this was in the first two years, with nutrition intergrated into basic science classes. Only 30 percent of medical schools surveyed required a separate nutrition course. This is an hour short of the American Society for Clinical Nutrition 1989 recommendation of 25h.

Distribution of the total number of hours of required nutrition education at US medical schools.
The question you have to ask, is how much do the doctors remember?


Adams, K. M.; Lindell, K. C.; Kohlmeier, M.; Zeisel, S. H. Status of nutrition education in medical schools. Am J Clin Nutr 2006, 83, 941S-944S.