Isn’t Science Wonderful? Obesity Talks to Cancer

A couple of week’s ago we looked at how being obese can give cancer a helping hand. I thought this would be useful as most people know there is a link but perhaps not much more than that. The message had two simple parts: (1) When we make extra fat cells they change the metabolism of our bodies through chemical signals that wander around and, in passing, can also drive cancer growth, and (2) Some of the extra fat cells congregate around tumours and give them direct positive vibes (i.e. other, local chemical signals).

But you may have spotted that I didn’t actually say what these ‘signals’ are – for the very good reason that we know rather little about them. Step forward, right on cue, Ines Barone, Suzanne Fuqua and friends from the University of Calabria and Baylor College of Medicine, Houston with a wonderful paper that’s just been published. Wonderful because it’s got so much data I’m green with envy but also because, like most excellent science papers, the key message is simple: normal cells that have moved into the neighbourhood can indeed talk directly to tumour cells. And the messenger is … leptin!

That’s astonishing. Even those with only a smattering of knowledge about how we work will know that leptin plays a key role in regulating energy balance. It’s a protein – a hormone – that circulates in our blood at levels roughly proportional to body fat. Its job is to signal the ‘full’ state, i.e. to reduce appetite. Somewhat perversely, obesity usually causes abnormally high leptin levels but it doesn’t work very well because the body has become resistant to its signal – much as happens with insulin in type 2 diabetes.

The new results show that leptin, released from nearby cells, can bind to cancer cells and make them do two things: (1) Release a chemical that tells the adjacent cells to send out even more leptin, and (2) Make proteins that help the tumour cells grow and invade.

There are a few wrinkles to these results. The study was on breast cancer cells with a particular mutation (in a receptor for the hormone estrogen) and the ‘groupies’ providing the leptin turned out not to be fat cells but fibroblasts – part of the supportive framework of cells and tissues – so they’re ‘cancer-associated fibroblasts’ (CAFs). And when the CAFs release leptin it floods out and the tumour cells embrace it and make yet more receptors for leptin to bind to on their surface.

But these details matter less than the key point: for at least some types of cancer cell a hormone often made in excessive amounts in obesity can signal directly to tumour cells, telling them to grow and spread. This doesn’t mean that all breast tumours, yet alone all cancers, respond to leptin. What it does show is that a key factor in obesity can talk directly to some types of tumour cell. It’s another example of the painstaking way in which science usually proceeds and, assuming the results are reproducible, we have one more little bit of the jig-saw.

Reference

Barone, I., Catalano, S., Gelsomino, L. et al. (2012). Leptin Mediates Tumor−Stromal Interactions That Promote the Invasive Growth of Breast Cancer Cells. Cancer Research 72, 1416-1427. 

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Fancy that?

Seeing as they started 28 years ago we can hardly blame members of the Harvard School of Public Health for publishing the results of their labours in tracking 120,000 people, asking them every few years what they’ve eaten and seeing what happened to them (a ‘prospective’ study). About one in five of the subjects died while this was going on but the message to emerge was that eating red meat contributes to cardiovascular disease, cancer and diabetes. The diabetes is non-insulin-dependent diabetes mellitus (NIDDM) or adult-onset diabetes – about 90% of diabetes cases. The cancers weren’t specified, although the evidence for a dietary link is generally strongest for colon carcinoma. The risk is a little higher for processed red meat than unprocessed.

How much?

Massive, if you mean the amount of data they accumulated from such a huge sample size followed over many years. If you mean on a plate, their standard serving size was 85 grams (3 ounces) for unprocessed beef, pork or lamb) and 2 slices of bacon or a hot dog for processed red meat. One of those a day and your risk of dying from heart disease is increased by about 20 per cent and from cancer by about 10 per cent – and the risks are similar for men and women. Just to be clear, that is a daily consumption – and the authors very honestly acknowledge that ‘measurement errors inherent in dietary assessments were inevitable’. They also mentioned that one or two things other than steak can contribute to our demise.

Are we any wiser?

If you recall from Rasher Than I Thought? the risk of pancreatic cancer is increased by just under 20 per cent if you eat 50 grams of processed meat every day. This report suggests that a limit of 1.5 ounces (42 grams) a day of red meat (one large steak a week) could prevent around one in 10 early deaths. So does it tell us anything new? Not really. Was it worth doing? Yes, because it adds more solid data to that summarized in Are You Ready To Order?

And the message?

Unchanged. Do some exercise and eat a balanced diet – just in case you’ve forgotten, that means limit the amount of red meat (try fish, poultry, etc.), stick with the ‘good carbs’ (vegetables, fruits, whole grains, etc.), cut out the ‘bad’ (sugar – see Biting the Bitter Bullet), eat fishy fats not sat. fats and, to end on a technical note, don’t pig out.

 References

Pan A, Sun Q, Bernstein AM; et al. Red meat consumption and mortality: results from 2 prospective cohort studies [published online March 12, 2012]. Arch Intern Med. doi:10.1001/archinternmed.2011.2287.

Pan A, Sun Q, Bernstein AM; et al. Red meat consumption and risk of type 2 diabetes: 3 cohorts of US adults and an updated meta-analysis. Am J Clin Nutr. 2011;94(4):1088-1096.

Biting the bitter bullet

The other day we took a short trip around obesity (Obesity and Cancer) in the course of which we noted that the former is a bad thing. So, you might say, they make a good pair – indeed they quite often come hand-in-hand, as obesity significantly increases the risk of quite a lot of cancers as well as other unpleasant conditions. The nasty effects include heart diseases and diabetes, a collection of problems often referred to as metabolic syndrome.

Fed up?

Obesity is usually caused by eating too much of the wrong stuff whilst parked on your rear end. True enough, but folk sometimes get a bit cheesed off by repeatedly being told to do something about it. As it happens, turning to Cheddar, if you can face the stuff, may actually help weight loss as cheese is high in protein and fills you up. And you might just go for that escape route when you’ve been leaned on by a recent article that, in effect, calls for draconian measures to limit the amount of sugar we eat. To be slightly more precise, the target is the USA because, as is well known, Americans lead the world in pretty well everything, including bad eating habits. The scientific dynamite propelling the charge is that sugar consumption worldwide has gone up three-fold in the last 50 years. The average American now eats over 600 grams of the stuff every day, a feat that leaves the rest of the world scarcely within range of a podium spot. It may seem a bit odd to be left trailing at anything by the most obese nation in the world (let’s leave Nauru –pop. 9265 – and a few other South Sea islands out of it)  but the link here is, of course, that sugar is a great source of calories and that the more calories you shovel down – in whatever form – the bigger you tend to become. But don’t get too cheeky about Yankee obesity as us Brits aren’t in great shape either.

Condensed facts

Very roughly an ‘average’ person needs about 2,100 calories a day. 600 grams of sugar would give between one third and one quarter of that total requirement. For an historical perspective that’s about 14 times as much sugar as the denizens of Great Britain were allowed during the second world war under rationing – a period when our diet is generally considered to have made us healthier than we’ve ever been. So you could say an element of control has been lost.

Calorific confusion

The ‘2,100 calories’ above are ‘food calories’, the unit sometimes used in nutritional contexts. It’s 1000 times bigger than ‘scientific’ calories, or gram calories (cal). Scientifically therefore, we mean 2,100 kilocalories (kcal). Which is why your fruit juice carton may tell you one glass contains 50 kcal. And, just to stop you asking, 1 calorie is the heat (energy) you need to raise the temperature of 1 gram of water from 14.5oC to 15.5oC.

An all-round view of the problem

Sugar consumption has ski-rocketed, eating too much of it unbalances your diet and bad eating habits can cause obesity and metabolic syndrome. But these things aren’t black and white: 20% of obese people have normal metabolism and a normal lifespan whilst 40% of those of normal weight will get metabolic syndrome diseases. So, whilst obesity indicates metabolic abnormality, it is not per se the cause.

The underlying science remains a matter of debate – a story well summarized by Gary Taubes. What is not in question is that we eat more sugar than we need and the real crunch is that sugar is like tobacco and alcohol – no, it doesn’t make you smelly or do Sinatra impressions – but it is addictive. It actually manipulates your pathetic brain cells so you keep asking for more.

On your Marx

So we’re seduced into eating more and more of something that can help us get fat and ill. What’s to be done? Lenin, who was fond of asking this question, would have dealt with it in a trice by limiting sugar supplies to one tenth of the dietary minimum and seeing who survived. Ah! The good old days. But the authors of the recent article had to come up with a pc 21st century equivalent. Of course! Taxation. And they’ve a point – you can tell people that smoking will give them lung cancer til you’re blue in the face but the only thing that stops them committing suicide is jacking the price up. Don’t ask me. Something to do with human nature. So it sounds like a good idea – but to have an effect on sugar you’d need a huge increase across a vast range of foods – fruit juice, ‘sports’ drinks, chocolates, sweets, cakes – forget it.

Do I have a solution? Of course! Bring back rationing. For all foods. Set at the UK second world war levels. Now we’d think about what we eat – carbohydrate, protein and fat – reverse obesity trends, solve world food problem, slash health service costs, cut queues at supermarkets (so they’d be normarkets). And we’d be rid of most of those damned cheffy t.v. programmes. Vote for me!!

Reference

Lustig, R.H., Schmidt, L.A. and Brindis, C.D. (2012). The toxic truth about sugar. Nature 482, 27-29.

Gary Taubes (2011). Is Sugar Toxic? The New York Times.