If you watched Horizon: Sugar vs Fat last week you will remember that in conclusion they seemed to decide that it was neither fat nor carbs that were behind obesity but fats with carbs. Dr Kenny talked very convincingly about his research into obesity and addiction, and we were left with the impression that cheesecake is the root of all evil.

That conclusion prompted a great question from one of my readers:

“The one important thing that seemed to come over from the programme, which I have talked about to other people, is that the real danger to our health is eating the fatty sugary things – ie cakes, biscuits, puddings etc etc. Is it also right to think that if we eat say a meal with fatty meat, starchy vegetables, then a pudding with cream and then cheese and biscuits, this will have the exact response in our bodies as eating say a sugary doughnut because we are feeding our bodies fat and sugar together, even if the sugar is produced by the breaking down of the starches? Or even just having a snack of cheese and biscuits…..Could we eat sugar and fat on alternate days?”

So what do we know?

First of all we need to say that the exact ratio of fats to carbs that suits your metabolism differs from one individual to another because, as you can see from the outside, we all process food differently on the inside. Our rate of digestion and gut transit differs from person to person, and so does the speed at which nutrients enter the blood stream. The hormones that control metabolism and appetite are also secreted in different amounts by different bodies. Some of us are more susceptible to the evils of cheesecake than others.

Once the nutrients are broken down and circulating in the blood, the body can’t readily distinguish between cheesecake or cheese and biscuits. It’s just a mixture of fats, carbs and proteins. So what’s going on?

Let’s look at how the body uses them:

We know carbs elicit a strong insulin response, and insulin is the master hormone that controls what happens next: fats are diverted into fat storage cells and combined into triglycerides, which stops them leaving the cell; glucose is shunted into the cells of the brain, organs and muscles to make energy, excess carbs are stored as glycogen. So insulin effectively makes any fat we eat unavailable for use by locking it away. That’s why insulin is sometimes called the storage hormone.

If you eat fats and proteins, but no carbs, you will secrete some insulin (enough to direct the amino acids contained in protein to the muscles) but not normally enough to cause insulin resistance, or to put fats beyond your reach for energy purposes.

Fats don’t trigger insulin release which leaves them floating free in the blood for your energy needs. Without insulin they remain in the form of free fatty acids (not triglycerides, which are a bundle of 3 free fatty acids joined together) which means they aren’t stored, so even if you do eat too much the body turns fats into ketones and excretes them.

There’s an important point to grasp here. It’s insulin that controls storage, not calories. Eat too many carb calories and you will store fat. Eat too many combined carbs and fat calories and you will store fat. Eat too many fat calories and you won’t. Crazy, eh? Just the opposite of what you’ve been told.

This fact is at the centre of the obesity debate and at the core of some very interesting research projects but this area was not brought into the Horizon debate. On the basis of what I have been reading during the last 18 months, most of the experts on the Horizon programme are hopelessly out of date. But that’s what happens when scientists become so obsessed with their own ideas that they fail to keep up with what’s going on elsewhere. It’s easily done.

I digress. Back to the question:

Some people produce too much insulin when they eat carbohydrates: the more carbs you eat, the more likely that is to happen (we clearly saw this with the carb-eating twin on Horizon); it also tends to happen with age. High insulin levels have been linked very clearly with many of the conditions we are trying to avoid, like diabetes and obesity. If you are one of those people who produces too much insulin then you have a problem when the carbs in your blood run out because the oversupply of insulin means fats stay locked in your fat cells, prompting you to eat again, even though you’ve just stored half a piece of cheesecake on your thighs.

This is where Dr Kenny’s research becomes interesting because if the next thing you eat is cheesecake (and he says that if there’s still some left in the fridge, you probably will) then you will keep on burning half and storing half of what you eat. That’s a sure route to obesity.

Dr Kenny’s research seems to indicate that we know when to stop eating, except when confronted with cheesecake and similar fat/sugar combinations. He is interested in why this happens. Is it a form of addiction? It seems this particular fat/sugar combination has a superior ability to overwhelm the brain’s reward circuits and seduce us into eating too much.

But we know from the Horizon programme that the person eating carbs with (almost) no fat also had poor appetite control, while the person eating proteins and fats knew when to stop eating. This points once again to sugar as the culprit. So, while that delicious 50:50 combination of sugar and fat was particularly irresistible, there are other factors too.

We can summarise that:

  • 100% carb – tendency to overeat, no stop button
  • 50% carb/50% fat – tendency to overeat, no stop button
  • 100% fat – appetite naturally curbed, know when to stop

Simple logic, therefore, tells us that the sugar is the more powerful partner in this deadly combination. There may indeed be a magic ratio that renders us completely powerless but that remains to be seen. I’m looking forward to reading more from Dr Kenny. I’d love to see some research that helps us understand this better.

So why single out cheesecake? Don’t all fat and carb combinations cause the same problem?

Well, for some people they do. Overeating cheesecake is something many of us can relate to, but some people experience a similar effect with only a very small amount of carbohydrate, enough to trigger insulin imbalances that trigger false hunger and lead to overeating. For these people any combination of carbs and fats are bad news, overwhelming your satiety hormones and leading you to overeat.

Here again, some carbs may be more problematic than others.

We know that white sugar is absorbed very quickly and causes an insulin spike. There is evidence that the gluten grains may cause a similar response and even stimulate the body’s opioid receptors. So there may be other ‘reward circuits’ in the picture, not just the simple feeling of high blood sugar. Fructose tends to enter the blood stream more slowly, but too much is a major cause of fatty liver disease. So it’s fair to say that sugars may be more of a problem than some of the other carbs but gluten is a close second, and I have a few clients who have a more than platonic relationship with potatoes. So, as I’ve said before, finding the carbs that trigger your overeating circuits is worth doing.

So… is cheesecake worse than cheese and biscuits?

It may be down to the delivery service. The fats in cheesecake are whipped and emulsified, and the sugars refined, which means they are more easily absorbed than cheese and biscuits. That may be an answer. It seems the brain lights up more brightly when the rewards are delivered more quickly. We know this from studying other addictive behaviour. But the exact ratio may also be important.

Just to add another nuance into the equation, quality of the fat you’re eating is also an issue for your health. Few would now argue that saturated fat is the problem we have been led to believe. By their very nature, saturated fats are more stable than unsaturated and they make ideal fuel for humans. Unlike omega 6 fats – the sorts of polyunsaturated fats that occur in intensively farmed meat and dairy and in sunflower oil and margarines – which, particularly when heated, are unstable in the body and can fuel obesity and inflammation. Hydrogenated fats are even worse.

So, to sum up, if you’re going to overeat (and most of us do) it’s safer to confine yourself to a high fat low carb diet. If you’re keeping within your energy limits, and maintaining your weight with ease, you should be OK eating both carbs and fats but… be aware that you may experience ‘false’ hunger signals if you’re insulin resistant; or you may be eating carbs for the wrong reasons – the ‘high’ rather than the hunger.

I recommend fine-tuning your processed food radar. Many things that we view as healthy are in fact processed. Have you ever walked past a wheat field and felt hungry? Of course not. But what happens when you smell toast cooking? The grains in our diet are highly processed – and hybridised. Cornflakes, even muesli, are processed foods, and if you’ve ever been to a sugar factory you’ll know there’s nothing natural about it. Our early ancestors wouldn’t have had much opportunity to raise their blood sugar: meat, milk, roots and shoots, leaves and berries are not capable of causing the blood sugar spikes that we tend to experience on a daily basis these days. If they found a hive of bees once a year they would have gorged themselves and then slept off the sugar rush. These days, we think nothing of spreading honey on toast and drinking fruit juice with it. It may seem natural to you but it isn’t, and it may prove lethal for some bodies.

The final point of the question – should we eat carbs and fats on different days? – that’s the basis of food combining and it works very well for some people. If your insulin sensitivity is in good shape then that could work well for you – but then you could probably also get away with eating both together.

If you suspect you are insulin resistant (and a spare tyre is a good clue) then it’s possible that even eating fats and carbs on alternate days may be too much for you – especially if you are in the higher BMI ranges.

As ever, it is down to individuals and if you continue to be concerned about this it would be good to get some expert nutritional advice.

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4 Comments on “Fats with carbs: what’s the story?

  1. Very interesting. The ‘Horizon’ point about the fat-and-sugar combination reminded me of the advice given by the nutritionist Hilda Cherry Hills (wife of Lawrence D Hills, the proponent of organic horticulture) in the early 1970s: the deadliest combination in food is that of fat and sugar. So it’s nothing new! Alas, my taste for cakes and biscuits (and, oh yes, cheesecake) won out over rational considerations, and the sad result is seen in my waistline.

  2. Hi, very interesting blog, the only think that kind of surpised me in the programme was that the doctor who was on the fat only diet ended up with higher insulin levels so does that suggest fat does result in an insuling response? i guess your body needs a mechanism to transport any kind of energy into cells?

  3. Good point. For a full answer to this question you could read my previous blog post but the potted answer is that the doctor on the high fat diet had higher insulin levels only after he had starved himself of all carbs for a month and then ingested an unusually high dose of glucose for the test. Even the most basic biochemistry knowledge of biochemistry would lead you to predict this outcome. It wasn’t the high fat diet that caused high insulin levels, it was breaking the diet. So no, fat doesn’t cause an insulin response and that test and the conclusions drawn from it were irresponsibly misleading. Free fatty acids permeate freely through cell membranes and into the mitochondria without the need for a transporter, whereas proteins and carbs do need some help. This fact alone should help us to understand what a natural fuel fats are.

  4. Thank you for such a comprehensive answer x

    On Thu, Feb 6, 2014 at 10:38 PM, Dawn Waldr

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