On Not Quitting Sugar
Fructose is the new saturated fat. Books, documentaries and websites put out a frightening story. Fructose—fruit sugar—is the evil half of table sugar. It is toxic, fattening and secretly added to our foods. It is so addictive, you may as well be using cocaine. Alarmed by these revelations, you conclude not quitting sugar would be irresponsible. A little reluctantly, you decide to cut out fruit. You pay $150 for an eight-week course to learn how not to eat sugar. You switch to glucose (the good half of table sugar!) to sweeten your food, but only a little bit. And when you do, your life transforms. The weight falls off (or not), and you become healthy, happy and energetic.
But we have been here before. As beautifully laid out by Alan Levinovitz, the fear of particular foods (dairy! grains! MSG!) does not come from science. The stream of news articles about the dangers of sugar does not reflect research results. Rather, this is a cultural cycle. At intervals, particular foods come to encapsulate our anxiety about modern life. We may live in an uncertain and dangerous world, but at least we can control what we put in our mouths. And it is tempting to believe there is one simple answer to all our health concerns. So if the information we are given is partisan or poorly vetted, we can easily buy into the latest scare.
This article offers an overview of the scientific state of play and provides a few reasons for not quitting sugar.
Assessing the Evidence
The main argument for not quitting sugar is that there isn’t any good reason to. Sure, on Google Scholar, you can find studies showing that rats fed high fructose become obese or get fatty liver or high blood pressure or diabetes. That’s fine, as far as it goes. But in terms of human nutrition, it doesn’t go very far. Rat studies use very high fructose levels to see these effects. This is only possible using purified fructose, which doesn’t occur in our diets. As a point of reference, a diet with 60% of calories from fructose can’t be achieved even by eating nothing but cane sugar (50% fructose) or high fructose corn syrup (55% fructose). When research is done at the fructose content of real human diets, the picture looks quite different.
Human studies over a range of fructose intakes (but without excess calories) show:
- fructose does not increase weight gain or blood triglycerides in normal weight or overweight individuals
- replacement of other carbohydrates with fructose has no detrimental effects on blood pressure
- fructose or other sugars do not increase markers of diabetes, uric acid or body mass index
- sugar intake is not a reliable predictor of tooth decay
- moderate fructose consumption may have beneficial effects on blood sugar control
But what about the new World Health Organization recommendations? Aren’t we all supposed to be cutting sugar to 5% of calories (6 teaspoons a day)? Indeed, those guidelines exist. But they have been criticized for relying on low-quality studies, and their stated goal is reducing tooth decay and obesity. Other official bodies have suggested much higher limits (10-25% of calories) or simply advise moderation without numerical targets. Given the lack of specific evidence for harm from fructose, public health efforts to restrict sugar consumption are probably premature.
OK, you think. So I’m not quitting sugar completely. But surely there isn’t a downside to cutting right back?
Actually, there are a couple of ways things could go pear-shaped.
One would be if you limit fruit intake. There is a current trend to tag fruits as high-fructose (bad) or low-fructose (maybe, if you’re careful). But it is rarely helpful to view food in terms of a single nutrient. Fruits can provide sugar, water, vitamins, minerals, phytonutrients, soluble fibre and resistant starch, all of which are good things. Even then, the benefits of whole fruit can go beyond the same elements recombined, for example by increasing satiety and aiding weight loss. Fruit also helps maintain beneficial gut microbes, and a diverse diet may reduce the risk of diseases like Type 2 diabetes. Eating a variety of fruits promotes the very goals you may have had in mind when you decided to cut back on fruit.
Another issue lies in restrictive eating itself. Checking the smoked salmon for added sugar might seem virtuous, but it could equally be a step on the path to disordered eating. We know that weight-loss diets tend to lead to long-term weight gain, and particularly in adolescents, can precede eating disorders. More broadly, restrictive eating can have unintended consequences. In a recent study, participants produced less of a hunger-suppressing hormone after a large dose of fructose, compared to glucose. Even so, they didn’t end up eating more—with one exception. Habitual dieters ate about 20% more after fructose, mainly as fat. There are additional mechanisms operating here, first to regulate appetite even when one particular hunger-suppressing hormone is low (in non-dieters), second to lose that regulation in the wake of conscious efforts to override it (in dieters). It is a cautionary tale.
How Our Bodies Use Sugar
There are many sugars in nature, including some you likely haven’t heard of, like xylose, rhamnose and arabinose. Our bodies don’t invest energy in recovering those sugars for our metabolism. However, we actively maintain systems for absorbing and utilizing glucose, fructose and sucrose (table sugar). It is worth laying out how this works under the conditions of normal metabolism.
We absorb glucose and fructose from the gut into the blood using separate transporter proteins for each sugar. If we eat sucrose, enzymes split it into glucose and fructose for absorption. From the blood, glucose can be taken up by any tissue, but fructose is taken up mostly by the liver. There, it is broken into two halves and reassembled as glucose, much of which is released to the blood. In this way, taking in fructose can increase your blood glucose (aka blood sugar). The two halves of fructose can also re-enter the blood as lactic acid, which our muscles burn for energy or use to make their own glucose. Outsourcing fructose conversion to the liver seems to be an efficiency measure, as there is much less fructose than glucose in the diet.
From a range of studies, we know about 50% of absorbed fructose is released from the liver as glucose and a further 25% as lactic acid. The liver stores 15-18% as glycogen (condensed glucose) and uses a portion directly for energy. It converts around 1-5% of absorbed fructose to fat for release, but at usual dietary intakes, this has little impact on fat levels in the blood. Either way, we burn about half the energy of fructose within 3-6 hours at rest, or 2-3 hours during exercise. The fraction burned increases even more when you eat fructose and glucose together.
Sugar in Sport
Knowing the effects of fructose on exercise gives you more reasons for not quitting sugar. If you practice endurance sport (something that might save your life), taking in a mixture of glucose and fructose is likely to aid performance. You may not end up breaking the Appalachian Trail record, but your staying power will almost certainly increase.
When you eat glucose and fructose together (e.g. as table sugar), glucose enters and leaves the blood rapidly, while fructose levels rise and fall more slowly. This happens for two reasons. Firstly, more insulin is released with glucose than with fructose, and blood sugar drops in response to insulin. Secondly, the two sugars have separate transport mechanisms, each with a maximum uptake rate. Due to these parallel pathways, carbohydrate enters the blood faster when both sugars are present, making more fuel available for exercise. In a cycling test, carbohydrates were burned 55% faster when both fructose and glucose were given, than with glucose alone. (Adding fructose also resulted in less gut discomfort.) A similar result was seen when fructose was given with maltodextrin. Accordingly, glucose plus fructose gave an 8% improvement in time trial performance in trained cyclists, compared to glucose alone.
Even taking in fructose between exercise sessions could have performance benefits. Fructose promotes glycogen storage in the liver, which is part of the process we know as carbohydrate loading. More glycogen in our muscles appears to increase the time to exhaustion during intensive exercise. The effects of glycogen in the liver are less clear, but like muscle glycogen, it may play a role in allowing you to maintain effort for longer.
Baking As A Gateway Drug
Beyond exercising, the one really positive thing you can do for your health is to prepare more of your food at home. For that habit to stick, it will help if you love what you are doing. Not quitting sugar opens up new possibilities here. It means you can learn to make strawberry balsamic thyme jam or hazelnut meringue biscuits or the country’s best carrot cake. If that gives you more confidence in your kitchen skills and imparts an enthusiasm for fresh flavours, who knows where that might take you? Perhaps you will plant a herb garden, or seek out a farmer’s market to get really fresh carrots, or simply feel less anxious about preparing food. In any case, food is more than nutrition. It is also cultural identity and pleasure and social interaction and mastery, all of which are important elements in our one short and precious life.
The enjoyment of sweet tastes is intrinsic to our biology, and the use and appreciation of sweet food has been cultivated since prehistoric times. Fructose is not a new or toxic element in our diets, but the fear of food certainly is. If you learn to ignore that fear—and the marketers of fear—you have a better chance of hearing and responding to your own body’s appetite signals. When that happens, you may pass up a piece of chocolate cake because you don’t feel like one right now. Then again, you might eat a slice because you’ve learned to trust your body, or because you are going for a big mountain bike ride in the morning and you want to fuel up. In either case, you’ll sleep better knowing the fructose story is just a beat-up.
And One More Thing…
The idea of sugar as addictive doesn’t really pass the giggle test. Try to imagine the World Health Organization suggesting that you limit crack cocaine to twice a day, or a New York Times journalist blogging about cutting out heroin for a month. You can also test it yourself. Put a bowl of sugar on the table and see how many times a day you can resist eating a big spoonful. If you’re still not convinced, you can read this article for a thoughtful analysis of the differences between drug addiction and ingestion of highly palatable foods.
Further Reading on Not Quitting Sugar
Sugar and Spice: Sweets and Treats from Around the World, Gaitri Pagrach-Chandra, Anova Books, London 2012. (Ideas for how to spend your time in the kitchen if you’re not quitting sugar.)
The Gluten Lie: And Other Myths About What You Eat, Alan Levinovitz, Regan Arts, New York, 2015
Why Diets Make Us Fat: The Unintended Consequences of Our Obsession with Weight Loss, Sandra Aamodt, Scribe Publications, London, 2016