Which is the preferred fuel: sugar or fat?

When I attended the big scientific conference on Pre-Diabetes and Metabolic Syndrome in Barcelona in 2007 (I have blogged about my clash with Dr Frank Sacks there previously), the program included a lecture by Dr Jesse Roth, a gentlemanly old professor, who had an impressive resume including significant work at the senior level of the National Institutes of Diabetes and Digestive and Kidney Diseases. He spoke about which came first, insulin resistance or hyperinsulinemia. In the course of his lecture, I thought I detected somebody who might be sympathetic to my interest in LCHF diets so at the end I approached him and asked whether the development of insulin resistance might be the cell’s defence against too much intracellular glucose. He responded, quite unequivocally, that the cell didn’t want to burn glucose but did so only because the body had to get rid of it. As often happens in these settings, somebody else intercepted him with another question before I had a chance to follow-up. Nevertheless, his comment got me thinking about one of the principle arguments that we hear in defence of dietary carbohydrates, that glucose is the preferred fuel of the cells in our body. This idea is often used to justify a diet high in carbs, even among people who have carbohydrate resistance.

It is true, when you present a range of fuels to the cells, glucose, fatty acids, protein, mainly, the cells will burn glucose first. From this we deduce that they do that because they prefer glucose. What if the opposite were true; that they burn it because they don’t like it and must dispose of it as quickly as possible?

Consider that, if you have a normal blood sugar, you have about a teaspoon of glucose in your blood. It’s not that much when you think about it. Your body likes to keep it in that range and will go to extremes to make that happen. If your blood sugar drops too low, you are at risk of impaired brain function, loss of consciousness and possibly death. This is what sometimes happens to type 1 diabetics who take too much insulin for the amount of carbs they have eaten. If you have a normal metabolism, your body has methods available to ensure this does not happen. If your blood sugar drops too low, you will release glucose from your glycogen stores and, if you deprive yourself of dietary sources of glucose, over time your liver will kick in with gluconeogenesis to convert protein to glucose.

On the other hand, if your blood sugar gets too high, your body goes to work to correct this problem, too. Consider that if you have an excess of as little as a half a teaspoon of glucose in your blood, over time that will cause serious harm. This is what happens in uncontrolled diabetes. Think of that for a moment – as little as a half a teaspoon of excess glucose will harm you over time. Does that not suggest that glucose is a toxic substance? Well your body thinks so because it goes to extraordinary lengths to keep your blood sugar in the normal range.

The primary agent that the body uses for this purpose is insulin. I am sure most are familiar with the idea that insulin is needed to let glucose into the cells so it can be burned. This is one way of disposing of excess glucose. It turns out that insulin has other ways to attack this problem, too. In the presence of high blood sugar and high insulin levels, the liver will turn glucose into fat. And, at the surface of the fat cells, when insulin levels are high, the fat that travels in the bloodstream in the form of triglycerides, is pushed into the fat cells and kept there. All this makes sense when you consider that it is done to keep glucose levels down in the normal range. It is pushed into the cells to be burned, it is turned into fat which is pushed into the fat cells where it can be kept out of the way so as not to interfere with the primary goal of burning off the glucose as quickly as possible.

Think again of that normal amount of blood glucose – one teaspoon. And consider what happens when you eat a typical high-carb meal. Let’s say you have a nice pasta dinner like the ones I used to enjoy in an earlier life. A big plate of pasta represents a lot of starch, all of which gets digested and absorbed as glucose. Add a nice foccacia bread which is also a starch. And for dessert, let’s have a big piece of apple pie a la mode (I used to make excellent pies). The crust of the pie and the sugar in the fruit and ice-cream all contribute to the flow of glucose from the gut into your blood stream. Ah, what the heck, let’s finish with a nice cup of coffee sweetened with a couple ounces of Bailey’s. Sounds pretty yummy, right? I used to eat like this all the time, right up to the point where I got type 2 diabetes.

Consider what is going on at the metabolic level when you eat a high-carb meal like that. Think of the amount of starch and sugar you have eaten which is quickly digested and flows into your blood in the form of glucose. There are many teaspoons of glucose in that meal. What you have done is you have created a metabolic emergency. Your body is desperate to keep your blood glucose in the normal range while your bloodstream is being flooded with glucose from that meal. You can imagine the work that insulin must do, and in fairly short order, to control this flood of glucose and to protect you from its toxic effects. It is no wonder that our metabolic systems break down as we continue to eat this way over the course of years, with the development of insulin resistance, hyperinsulinemia and, eventually, for a lot of us, type 2 diabetes.

Now, consider the possibility that we weren’t meant to burn glucose at all as a primary fuel. Consider the possibility that fat was meant to be our primary fuel. In my current state of dietary practice, I am burning fat as my main source of energy. My liver is converting some of it to ketones which are needed to fuel the majority of my brain cells. A small fraction of the brain cells, around 15%, need glucose along with a few other tissues like the renal cortex, the lens of the eye, red blood cells and sperm.Their needs are met by glucose that my liver produces from proteins. The rest of my energy needs are met with fatty acids and these come from the fats I eat.

If you have seen my earlier posts on physical stamina, you will know that I believe my exercise capacity is certainly much better now than it ever was when I was eating a high-carb diet and depending on glucose for my fuel. There is evidence that the brain, when burning ketones, is more efficient than when it is burning glucose. Less oxygen is needed to produce ATP, the energy molecule, when burning ketones. It also appears that when burning fats and ketones, the problem of excess oxidative stress is resolved. Oxidative stress is being implicated in a host of pathological conditions and may very well be the common factor that explains why serious diseases like cancer, heart disease and diabetes are linked. I also know that my inflammatory markers are very low on a low-carb high-fat diet. We know that there is an inflammatory underpinning to chronic diseases of all types. The inflammation and oxidative stress problems are linked and there is a bit of a chicken and egg issue there in terms of which causes which. It is somewhat moot, however, when it comes to a LCHF diet since both are profoundly reduced.

Another way to look at the question of whether fat is the preferred fuel is to ask yourself, in what form does the body store fuel? We store some glucose in the muscle and liver in the form of glycogen. This is available in times of acute stress as a fast source of emergency fuel but it doesn’t last very long. Our glycogen stores are quickly depleted. The long term storage form of fuel is fat. We store both the fats we eat and the carbs that our liver converts to fat in our adipose tissue. When we need to access that fuel, we release it as fatty acids and burn it as such. We don’t convert it into glucose. This implies to me that the body prefers fat over glucose.

If you accept that we were meant to eat primarily fat rather than carbs, then the question arises as to whether different types of fat are better than others. We have long been admonished about the dangers of saturated fat because of the purported causal link to heart disease. Saturated fats are those that tend to remain solid at room temperature. Butter, coconut oil, bacon fat, lard and the fats on meat are examples of fats that have high proportions of saturated fatty acids. Recently, however, the evidence that supported this idea has been under attack and there is newer  and more convincing research showing that, not only does dietary saturated fat not cause heart disease in general, certainly in the context of a low-carb diet it may actually improve your cardio-metabolic risk profile. At the same time, meta-analyses of research on fat consumption and obesity rates are confirming that fat in the diet is not the cause of excess body fat.

On the other hand, the vegetable oils that we have been encouraged to eat in place of saturated fats, are being implicated in the rise in chronic disease. Remember that inflammation is an important underpinning of chronic diseases of all types. It turns out that the vegetable oils that have become ubiquitous are very rich in omega-6 fatty acids and these are implicated in the promotion of inflammation (this is why you are advised to avoid most vegetable oils with the exception of olive oil and canola which are relatively low in omega-6). So, it is important to consider which fats and oils you are eating after all but not in the way most people think.

One last piece of this puzzle fell into place for me when I collaborated with my friend and colleague, Dr Steve Phinney , to study a popular west coast traditional food, oolichan grease. The west coast First Nations people ate a traditional diet that was high in fat and low in carbs. An important part of this diet was a unique marine oil. They have been harvesting the oolichan fish and rendering and eating its fat for centuries, if not millennia. It is a big deal. In modern times there is a lot of work involved so in the old days, before there were powered boats, modern nets and other technologies, the oolichan harvest represented a huge undertaking. Whole villages moved to the oolichan camps along the rivers in which the fish would spawn and they would stay there for months catching and processing the fish. When the oil was extracted it was stored in water-tight bent-wood cedar boxes and was remarkably durable. It was highly valued as a staple food and was traded inland to populations who didn’t have access to the fishery. “Grease trails” were established through the coastal mountains for this purpose and there are accounts from early explorers who reported seeing whole villages trekking inland with everyone carrying boxes of grease to trade.

The question that intrigued us was why did they go to all that effort to render the fat from that particular fish when there were other abundant sources of fat available in this environment? There were sea mammals like whales, seals and sea lions. There were land mammals like moose, deer, elk and mountain goat. There were other fatty fish like salmon, herring and halibut. Yet, for some reason, going back into ancient times these people went to great lengths to extract the oil from that one particular little fish.

We think we got the answer when we had the grease analyzed in the Minnesota lab of our friend and colleague Dr Doug Bibus.  It turns out that the fatty acid profile of the oolichan grease is remarkably similar to that of human fat. That is at once a startling and revelatory discovery. If the body’s preferred fuel is fat, then it stands to reason that when the body stores fat it would do so with the fatty acid profile it prefers to burn. It follows then, that if you are burning fat from your diet, the preferred dietary fat would be the one that has a similar fatty acid profile to the one you store. These ancient people figured out that the fat from the oolichan fish was the most preferred fat from all the choices they had in their environment. And, they did this without the use of a gas chromatograph! This is a wonderful story of ancient dietary wisdom that helps advance our understanding of current dietary science. The coastal people figured out that their low-carb traditional diet was highly sustainable when they ate the fat that most resembled their body fat. This strikes me as an important clue to the puzzle of how to sustain a modern LCHF diet.

After we completed our study of oolichan grease which resulted in the publication of a scientific paper, Dr Phinney concocted a faux oolichan grease for his own use. He mixes one part butter, two parts olive oil and one part canola oil to approximate the fatty acid profile of the real oolichan grease. He stores this in his fridge and uses it for all his cooking needs.

The key to sustaining a LCHF diet is in the fats. You need to get comfortable with fat consumption in general and saturated fats in particular and you need to avoid the high omega-6 oils.

We were meant to burn diesel, not gas.

Phinney SD, Wortman JA, Bibus D. Oolichan grease: a unique marine lipid and dietary staple of the north Pacific coast. Lipids. 2009 Jan;44(1):47-51

9 thoughts on “Which is the preferred fuel: sugar or fat?

  1. Fantastic summary.

    I also came to the conclusion that the better interpretation of the evidence is that insulin-driven use of glucose is a triage response of the body and not evidence that glucose is the preferred fuel. Glucose is only preferred fuel in the sense that it is preferable to burn it than allow excess glucose to cause glycation damage to tissues and membranes. I always find it remarkable how limited scientists can be in their interpretation skills.

    I am curious as to the butter-olive oil-canola oil in the ratio of 1:2:1. Canola oil, based on the Nutrition Data website, is about 5:1 monounsaturated (18:1) to omega 6 (18:2 n6). I gather, therefore, that the canola is for a limited amount of essential omega-6, since the olive oil is already a good source of monounsaturated fat. But as I am having 10 grams of almonds and 10g of walnuts with breakfast, I would already get some omega-6 and I expect I would not need the canola oil for essential omega-6. I would prefer to avoid as much processed oil as possible.

    Dr Jay’s Reply:

    There are indeed other sources of omega-6, like the nuts you mention. The main point is that the ratio of omega-3 to omega-6 not get too far out of whack. As I understand it, the ideal ratio should not exceed 1:3 whereas most people are in the range of 1:20 to 1:30 due to the heavy use of the high omega-6 vegetable oils. I know you are very careful about your diet so I expect you would be able to figure out what is your ratio now and determine from that whether you would be okay adding canola. I understand that many people feel it is important to avoid the highly processed oils including canola. I am somewhat agnostic on that although, at the same time, I don’t actually eat much canola myself. What I do get tends to come from food products made with canola like Hellman’s mayo.

  2. Avocado Aioli Butter

    I did some experimenting in the kitchen today to concoct my own version of Oolichan grease, using the 1:2:1 butter/olive oil/canola oil as a guide. I started with a ripe avocado (not overripe–I find ripeness peak at about 5 days after getting them rock hard at the grocer). I pureed the avocado with my Bamix handheld blender and then blended in a couple of cloves of roasted garlic. Roasted garlic is a good emulsifying agent. It was a large avocado so I added three cloves. Then I blended in one part butter followed by two parts extra virgin olive oil, until I got the texture I wanted. The ratio was about 1:2:1 of butter/olive oil/avocado oil, guessing at the oil percentage of the avocado pulp. The butter was a really nice local churned butter, >86% bf made from creme fraiche (i.e., cultured and creamy). I added salt and pepper to taste.

    My wife was the taster and she raved.

    My aversion to canola oil is mostly a concern about oxidation of the omega-6 oil. Extra virgin olive oil, good butter and fresh avocados have plenty of fat-soluble antioxidants to reduce oxidation of the fats.

    I am also wary about adding variable amounts of omega-6. Phinney and Volek (Art and Science of Low Carb Living) make the point that the need for omega-3 and omega-6 go down on low-carb and that they should be viewed as vitamins instead of fuel. It seems from this that the fat you eat in variable amounts for energy (such as my avocado aioli butter), need not have omega-6, so long as a sufficient amount is in a fixed dose in the diet. Hence I think I would be covered with my fixed portion of nuts with omega-6 (I also have macadamia and hazelnuts). So I chose avocado over canola oil, which gives a pleasing flavour and texture and accomplishes close to the same fat profile.

    Dr Jay’s Reply:

    Sounds delicious!

  3. Whenever someone tells me that glucose is the preferred fuel because we burn it first, I tell them that we burn alcohol before anything else. Using that logic, we should all be hocked up on liquor 24/7 . What makes real sense though, is that the body will metabolize the most toxic fuels first.

    Dr Jay’s Reply:

    Good point!

  4. The analogy to alcohol is instructive. The body produces a small amount of it, so the body knows how to metabolize it. If one starts drinking more than a modest amount regularly, the body upregulates its processing of alcohol, so a regular drink can hold his drink, so to speak. Someone like me who typically has just a small glass of wine with dinner on the weekends can’t have two glasses without getting drunk. But drink too much too long and things break down, like the liver, and tolerance for alcohol is lost.

    People who consume more glycemic carbohydrates than low carbers perform better on glucose tolerance tests. This is often interpreted as evidence that a high-fat diet is bad. But, using alcohol as a guide, this really shows the body bolstering its metabolic defences. But eat too much too long and things break down, like the liver, and tolerance for carbohydrates is lost.

    The body seems to upregulate with fat consumption, as well, becoming keto-adaptive. But the difference is that there is no indication the upregulation burns out over time. Rather, there seems to be a limit on bile production, so that the body does not absorb more fat from the gut than required, unless the cell to liver signalling is disrupted by excess dietary carbohydrates……

    Dr Jay’s Reply:

    Dr Otto Schaefer was a famous physician who spent his career in the Arctic administering to the Inuit. I had the good fortune to meet him when he was retired and in his nineties. We had a far-ranging discussion about his largely unsuccessful attempts to alert the world to the terrible health consequences of the diet transition from a HFLC traditional diet to the high crap diet eaten today. I remember him still bristling with anger when recounting incidents when non-diabetic Inuit, when sent to southern hospitals, would return on insulin, having failed their OGTT’s.

  5. Tansi, Hello, it is Darren, I just got out of Biology class and the lecture was on saturated fats and my Professor show us this video. Very interesting, exactly what you were saying and with credible sources. Check this one out if you have not seen it yet!

  6. Pingback: What’s Our Preferred Fuel? | Paleo Diabetic

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