Sweet Love …

 

Sweet love, renew thy force; be it not said

Thy edge should blunter be than appetite,

Which but to-day by feeding is allay’d,

To-morrow sharpen’d in his former might:

No prize for knowing I didn’t write those lines — or even that they’re down to The Bard of Avon. What he was on about here is the distinction between genuine (sweet) love and lust (appetite), the problem being that the latter may be assuaged today but will surely return tomorrow. Had we, by some Star Trek-like device, been able to secure his services for this piece, Shakespeare, master of the double-entendre, would quickly have spotted an opportunity in his new role as pop-sci scribe. For sweet read sugar: for appetite addiction.

Gary Taubes considers sugar to be the root of most western illnesses. Photograph: Alamy

The combination can be toxic, as the estimable US journalist Gary Taubes has argued over the last 15 years. His latest book The Case Against Sugar has just come out and I’m keen to give it a plug. In so doing I should point out that we’ve also done our best in these pages to make the same case — particularly in relation to cancer. However, it’s a little while since we wrote specifically on sugar, diet and cancer, mainly because nothing really new has caught my eye. Reading again the most relevant of our blog stories I thought they did a pretty good job (as Shakespeare might have said, being a chap not known for modesty). Three I thought worth looking at again are:

Biting the Bitter Bullet: how obesity and cancer quite often come hand-in-hand and how it is that we’re seduced into eating more and more of something that can help us get fat and ill.

A Small Helping For Australia: makes the point that this is a global problem (even though Australia’s wonderful).

The Best Laid Plans in Mice and Men..: artificial sweeteners aren’t the solution – just another problem.

Actually, there is one recent result we might mention — from Ken Peeters, Johan Thevelein & colleagues at the University of Leuven. Bearing in mind the long-established ‘Warburg effect’ by which cancer cells switch the energy supply system that breaks down glucose from respiration (using oxygen) to fermentation (making lactate), they looked at yeast cells that grow fastest when they ferment — much as cancer cells grow quicker than normal cells. Rather remarkably, they discovered a hitherto unknown way in which fermentation links to a key pathway controlling cell proliferation. That pathway centres around a protein called RAS that we met in Mission Impossible.

This finding does not show that eating lots of sugar gives you cancer but what it does show is a way by which, if yeast cells ‘eat’ more sugar, they grow faster. It seems quite possible that the underlying mechanism might work in human cells (the human version of the protein that links sugar metabolism to RAS, called SOS1, works in yeast) — giving an explanation for the well-known fact that the more sugar you eat the fatter you are likely to become. And what we do know is that obesity does raise cancer risk.

I dare say Gary might reckon this result worth a footnote in the second edition of: The Case Against Sugar by Gary Taubes is published by Portobello Books (£14.99).

Reference

Peeters, K. et al., (2017). Fructose-1,6-bisphosphate couples glycolytic flux to activation of Ras. Nature Communications 8, Article number: 922 doi:10.1038/s41467-017-01019-z.

Advertisements

Fast Food Fix Focuses on Fibre

If you’re like me you’re probably more bored than absorbed by the seemingly continuous stream of ‘studies’ telling us what we should and shouldn’t eat. No one’s going to argue it’s unimportant but gee, I wish they’d make their minds up. Of course the study of diet and its effects is tricky – as we noted in Betrayed by Nature – not least because you generally need enormous numbers of people to tease out significant effects.

Fortunately authoritative sources like The American Heart Association offer generally sane and simple advice: “eat a balanced diet and do enough exercise to match the number of calories you take in.”

A balanced diet includes fibre, sometimes called roughage, the stuff we eat but can’t digest that assists in taking up water and generally keeping our insides working. There’s much evidence that eating plenty of fibre helps to prevent bowel cancer – usually accumulated from vast numbers (e.g., the European Prospective Investigation into Cancer and Nutrition study involved over half a million people from ten European countries). But even for fibre, when you might just be thinking the answer’s clear-cut, there are other studies showing no protective effect.

So hooray for Stephen O’Keefe and friends from the University of Pittsburgh and Imperial College London for coming up with a dead simple experiment – and some pretty astonishing results (though to prevent panic we should reveal at the outset that they confirm that a high fibre diet can substantially reduce the risk of colon cancer).

Doing the obvious

The experiment compared what happened to two groups of 20, one African Americans, the other from rural South Africa, when they swapped diets for two weeks. So, in principle ‘dead simple’ but to describe it thus does a great injustice to the huge amount of effort involved – for a start they had to find two lots of 20 volunteers willing to have a colonoscopy examination before and after the diet swap. The Western diet was, of course, high protein, high fat, low fibre, whereas the typical African diet was high in fibre and low in fat and protein. Just to be clear, the American diet included beef sausage and pancakes for breakfast, burger and chips for lunch, etc. The traditional African diet comprises corn based products, vegetables, fruit and pulses, e.g., corn fritters, spinach and red pepper for breakfast.

B'fast jpegCompare and contrast.

A rural South African diet (corn fritters for breakfast) and the American diet (Getty images)

Shock – and horror

Almost incredibly, within the two weeks of these experiments there were significant, reciprocal changes in both markers for cancer development and in the bug army – the microbiota – inhabiting the digestive tracts of the volunteers. That is, the dreaded colonoscopy revealed polyps (tumour precursors) in nine Americans (that were removed) but none in the Africans. Cells sampled from bowel linings had significantly higher proliferation rates (a biomarker of cancer risk) in African Americans than in Africans. After the diet switch the proliferation rates flipped, decreasing in African Americans whilst the Africans now had rates even higher than in the starting African American group. These changes were paralled by an influx of inflammation-associated cells (lymphocytes and macrophages) in the now high-fat diet Africans whilst these decreased in the Americans on their new, high-fibre diet.

Equally amazing, these reciprocal shifts were also associated with corresponding changes in specific microbes and their metabolites. You may recall meeting our microbiota (in The Best Laid Plans of Mice and Men and It’s a Small World) – the 1000 or so assorted species of bacteria that have made you their home, mostly in your digestive tract, of which there are two major sub-families, Bacteroidetes and Firmicutes (Bs & Fs). We saw that artificial sweeteners in the form of saccharin shifts our bug balance: Fs down, Bs up. Here feeding Americans high-fibre diet was associated with a shift from Bs To Fs. As we noted before, the composition of the bug army is important because of the chemicals (metabolites) they produce – in this case the diet switch resulted in more short chain fatty acids (e.g., butyrate) in the American group and a reciprocal drop therein for the Africans.

The bottom line

It really is quite remarkable that these indicators of cancer risk manifest themselves so rapidly following a change to a typical Western diet. Of course ‘markers’ are one thing, cancer is another. As one of the authors, Jeremy Nicholson of Imperial College London, said: “We can’t definitively tell from these measurements that the change in their diet would have led to more cancer in the African group or less in the American group, but there is good evidence from other studies that the changes we observed are signs of cancer risk.”

Put less scientifically, “a nod’s as good as a wink to a blind horse.”

Reference

O’Keefe, S.J.D. et al. (2015). Fat, fibre and cancer risk in African Americans and rural Africans. Nature Communications 6, Article number: 6342 doi:10.1038/ncomms7342