Starch is Effectively a Sugar – But Food Micronutrient Insufficiency May Be the Real Culprit in Obesity Related Disease
23 January 2013
It constantly amazes me that in the discussion on sugar being a major cause of ‘diabesity’1, in this issue of the BMJ, and over the years elsewhere, that basic physiology moves out of the picture. Starches are polysaccharides which are easily broken down or hydrolysed to constituent simple sugars; a common starch is amylose which becomes glucose, releasing a small amount of energy, when acted on by the enzyme amylase. Interestingly, amylase is even present in human saliva, and in high amounts in some human groups2, in addition to pancreatic secretions. One can taste the increasing sweetness of glucose on chewing tasteless white bread, which is unlikely to be good for teeth3. Breads, rice and white potatoes, our so-called staple foods, provide starch with a high glycaemic index and load, which may be greater than sucrose4. The sugars (monosaccharides) are absorbed extremely quickly, raising blood glucose to high levels, and releasing large amounts of energy for use or storage. Willet and Ludwig(1136/bmj.e8077)5 acknowledge this fact about starch in their commentary in this issue.
Pre-agriculture, 10,000 years ago, starchy food was scarce; tough, stringy roots and tiny grains. Subsequently, these tubers and grains have been bred to produce greatly increased volumes and proportions of starch6, and sugars, which preserve, pack and travel well. Baked breads and crackers, even of the ‘whole grain’ type, contain much refined flour. Whilst many clinicians advise whole grain based foods as part of a ‘prudent diet’ which confers health benefits, when studied, cardiovascular risk markers did not improve on a whole grain augmented diet7 8. Non fruit sources of mono- and di- saccharides (fructose, sucrose) such as from maise, sugar cane and beet, have also been highly bred for their rich energy yield. This whole group of refined starches and sugars is highly implicated in energy dense food addiction9.
On the other hand, humans evolved from a ripe fruit-eating primate, approximately 20 million years ago, and generally apes (except gorillas) have continued to eat a high energy plant diet of seeds and fruit, probably helping to supply the enlarging, energy-demanding brain10. It appears that when fruit sugars are ingested with fibres and other complex plant chemicals, it is absorbed at a slower rate. Whilst fruits may have been cultivated to be fleshier and contain more sugar they can still be eaten whole, often with skins and seeds, which appears to contribute to their low glycaemic index. Even preserved (dried, frozen), they retain fibre and unknown types of plant nutrients. Notably, it is important that these food constituents are eaten as food. As the meta-analysis of Myung et al (1136/bmj.f10)11, also in this issue, shows, vitamins and supplements are not effective at preventing cardiovascular disease (CVD).
Yudkin’s book ‘Pure White and Deadly’ mentioned by Jackson (1136/bmj.f307)12 and Watts (1136/bmj.e7800)13 could refer to both sucrose and starch. We may have to face the fact that refined starches should be treated as refined sugars and that to decrease diabesity rates, consumption of ‘high (refined) carb’ diets needs to be severely curtailed, probably aided with addiction management in the already centrally overweight.
However, adequate dietary energy for modestly active, older or overweight and/or diabetic individuals can be replaced with plenty of low-processed fruit, vegetables, oil seeds/nuts14 and free range animal products, which are also known to confer health15 16. Rapidly, such a diet rights the wrongs of severely unbalanced micronutrient to macronutrient ratios. Micronutrient insufficiency seen in diabesity17, or rather malnubesity18, decreases. Such diets reduce the central obesity related metabolic syndrome continuum of CVD, diabetes and cancer risk.
So, appetising sugar and starch laden foods indirectly cause obesity by energy overload, as well as effectively displacing food micronutrients needed for healthy metabolism.
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Competing interests: None declared
General Practice and Primary Health, School of Population Health, University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand
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