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Understanding Sugar and How it Impacts Our Behaviour

Before I got into long distance running, I honestly had no idea how to go about nutrition and I am still a beginner. Like most marathoners, I basically upped my carb intake one week before the race with pasta, white rice, bagels and oatmeal and fueled my long runs on energy gels, ate lean protein like eggs, fish and chicken, cut down on fatty foods or anything with too much fiber to avoid GI distress. I've also taken a few other supplements based on doctor's recommendation.

My runner's diet doesn’t look that bad, right? I thought I was doing well, but not really. I hear that sugar causes inflammation and I am eating more highly processed carbs than necessary. I am keen to figure out a way to eat more fresh whole foods and crowd out pasta, white breads and refined sugar. So far I have been impressed by a few delicious, nourishing whole foods recipes, just look at those iron rich, guilt-free Double Chocolate Teff Cookies!

Recently I stumbled across a video lecture which went viral in 2009. It's called Sugar: The Bitter Truth by Dr. Robert Lustig. I like it so much that I watched the video twice in one day. I have just finished his book Fat Chance: Beating the Odds Against Sugar, Processed Food, Obesity and Disease. I find the video very entertaining and educational, and the book is just as fluid in explaining the biochemical relationship between obesity, hormones and metabolic syndrome.

For me the key takeaway is that the biochemistry (hormones) dictates our behavior and determines our food intake or cravings. Our eating behavior is driven by three different types of signals to the brain: hunger, reward and stress. An important way to alleviate or "fix" our eating hormonal problems is to bring our insulin levels down by reducing sugary food intake and improve our insulin sensitivity by taking in fiber and perform greater physical activities.

My personal takeaways from the book on Sugar and our biochemistry

There is so much practical information in this book. I've decided to blog a few interesting takeaways and action points which can complement my IIN health coach training.


Insulin is a energy storage hormone. After food intake, blood glucose level rises, the pancreas responds by releasing insulin to get the liver to work. The liver burns some of the glucose, sending the rest to be burned by muscle and fat tissues in the body. Any glucose not burned is converted into glycogen (starch) for storage in the liver and skeletal muscles. Any further glucose not stored as glycogen is converted into triglycerides (fat molecules) to be stored in fat cells. Insulin basically sweeps sugars from the blood and encourages excess energy to be stored as glycogen or fat.


Leptin is a hormone made by fat cells. It sends satiety signals to the hypothalamus that the body has enough energy storage, in order to control food intake and to maintain energy balance and a stable weight. Unfortunately leptin signaling can fail, either due to (i) leptin deficiency when the fat cells are not producing enough of it, or (ii) leptin resistance when the hypothalamus fails to see the signal. When leptin signal fails, the brain thinks the body is starving and tries to reduce energy expenditure (move less) and increase energy storage (eat more), leading to weight gain.

Obesity and Starvation feel the same

Interestingly, an obese person can share similar symptoms with a starved person, such as fatigue and depression. In both cases the brain fails to see and respond to the leptin signal. In the case of starvation, it is driven by leptin deficiency. In the case of obesity, it is due to leptin resistance.

Reward and Pleasure

Insulin and leptin also play important roles in the brain's reward and pleasure center. Dopamine is a neurotransmitter associated with reward seeking behavior. As we consume a delicious meal, we experience a sense of reward as dopamine is released and binds to a specific dopamine D2 receptor in the reward center. Anything that increases dopamine provides a greater sense of pleasure.

As a normal individual eats, blood glucose rises, insulin is released (by the pancreas) which clears away dopamine from the synapses, thus removing the feeling of reward. This is when the individual feels satiated. Similarly, when leptin is released, a signal is sent to reduce the release of dopamine, which reduces the sense of reward from food consumption and prevent overfeeding.

For insulin and leptin resistant individuals, the brain doesn't see the signal when dopamine is not cleared from the synapses. The individuals would continue to experience reward from food consumption even when the body has stored enough energy. The need to seek reward and for food consumption persists, leading to overeating and weight gain.


Cortisol is an interesting and very important hormone, as we all need it to stay alive. Whilst small quantities of cortisol from physical activities are great for your health, chronic exposure can be detrimental as it leads to higher blood pressure, higher blood glucose level and visceral fat or "big belly" fat storage. Visceral fat and fat deposits in the liver causes insulin resistance and can lead to cardiovascular disease and metabolic syndrome.


Sleep deprivation can increase cortisol and leptin levels, making the brain think the body is starving, leading to over-eating. Just remember the last time you were staying up late for work or for an exam or extremely jetlagged, did you cave in to anything that was high in sugar and fat?

Insulin Resistance

Insulin resistance takes place when the body stores more fat in the liver, the liver cannot work properly. The pancreas then releases more insulin to make the liver work harder. This in turn encourages further fat storage, increase weight gain and the risk of obesity. High insulin levels also promote high blood pressure, high blood lipids and the risk of a heart attack or stroke. The fat in the liver also causes inflammation, which drives further insulin resistance, liver scarring and non-alcoholic fatty liver disease.


Fructose is a type of sugar commonly found in soda, high fructose drinks and fruits. Fructose can be found in table sugar or sucrose, which is roughly half glucose and half fructose. Whilst glucose can be metabolized by every cell in the body including liver, muscles and even the brain, fructose does not turn into glycogen and is metabolized directly into fat, which can promote heart disease. Fructose can also cause inflammation, insulin resistance, higher blood glucose levels and eventually diabetes. The intake of fructose does not raise blood glucose level, and does not trigger the release of insulin (in fact, fructose has a very low glycemic index), nor does it reduce the hunger hormone ghrelin. This means drinking a large can of soda would not diminish your appetite for food. Fructose is essentially empty calories.


Soluble fiber (e.g. psyllium) absorbs water to form a sticky gel which helps to slow digestion and absorption. Insoluble fiber (e.g. polysaccharides, cellulose) helps food to move quickly and reaches the small intestine sooner where the satiety hormone PYY is released. A slower absorption of glucose means a slower increase in blood glucose to keep your insulin down and result in less fat storage. As mentioned at the beginning, insulin is a energy storage hormone, a lower and more stable insulin means less fat storage and more capacity to burn fat.

So, which diet makes the most sense?

In the book, Dr. Lustig walks through some popular diets such as Low Fat, Atkins, Vegetarian/ Vegan, Mediterranean, Paleolithic, and Ornish. The most successful diets tend to be low in sugar and high in fiber, fat and carbohydrate are consumed together with an offsetting amount of fiber.

Action Points for Self

Eat Real Food like fruits and vegetables which contain lots of fiber and nutrients to crowd out processed foods. Real food means food that doesn't bear a company logo, and food that your grandmother would recognize. These will likely to be low in sugar (to prevent insulin resistance), high in fiber and low in trans fat. Real food generally comes with more fiber, which helps food to move through the intestine faster and the satiety hormone PYY can kick in sooner to stop you from overeating.

Drink More Water to crowd out soda. Drinks should not have more than 5 calories, except if it is milk. You can set a reminder to drink water regularly, or get an app to help you track your water drinking.

Eat Whole Fruits. It is fine to eat whole pieces of fruits even if they contain fructose because they come with fiber, vitamins and nutrients and lots of water which fills you up.

Eat Breakfast. Having breakfast helps to reduce ghrelin (the hunger hormone) and provide the energy needed for oxidation of fat (fat burning). It is a good idea to eat some protein for breakfast as it uses up more energy to digest protein compared to carbohydrates and protein causes less of an insulin spike compared to carbohydrates. Protein also helps to reduce ghrelin more than fats and carbohydrates, which keeps you satiated for longer during the day.

Eat Good Fats such as olive oil, flaxseed oil, fish rich in omega-3 fatty acids, which are anti-inflammatory and protective against heart disease. Avoid omega 6 fats and trans fats such as margarine and canola oil because these cannot be completely broken down by our bodies.

Enjoy Dessert. The book suggests that we make dessert special and an occasional treat. I'd like to add a few more suggestions such as sharing desserts with friends so you don't overindulge. If you are still hungry after the main course, consider ordering a second starter or a side vegetables. I have done that before, it's a little strange to have starter as dessert but you are a paying customer so do what you want and what is good for your health.

I'd also like to share a Carrots N' Cake blog on how to beat sugar addition. The advice is to have plenty of real food, high quality protein, healthy fats, grains, fruits and vegetables. If you are truly satisfied and nourished from your main meal, you will less likely crave dessert.

Shopping at a Supermarket

Look for food that will spoil and real food that doesn't have a Nutrition Facts label. You will likely end up with foods full of fiber and micronutrients. If the food has a Nutrition Facts label, by definition it is processed. If it is shelf stable, bacteria wouldn’t want to eat it and you shouldn’t either.

Look out for Hidden Sugar

Food manufacturers are very clever at hiding sugars on food labelling and there are at least forty other names for sugar. Examples of sugar that contains fructose: Agave nectar, Florida crystals, Panocha, Cane Juice crystals.

Eating out

Try to eat real food as much as possible. Have water instead of soda. Ask the server not to put bread on the table. Swap salad for fries. Share with a friend if the portion sizes are large.


Exercise does not cause weight loss but it brings about huge amount of health benefits. Exercise helps build muscles and muscles can help to improve your metabolic rate at rest. Exercise helps to improve insulin sensitivity as well as leptin signalling, so the body can better regulate its energy balance. While exercises temporary increases cortisol levels, they reduce quickly and remain low for the rest of the day. Exercise also releases endorphins which make you feel good. That's also why I love running so much!

Thank you if you have made this far into the blog. I hope find this topic interesting. Please share any feedback or thoughts or personal experience on your relationship with food and/or sugar. I would love to hear from you.

Sources of information

  1. Sugar: The Bitter Truth, Video lecture presented by Dr. Robert H Lustig, MD, UCSF Professor of Pediatrics in the Division of Endocrinology,

  2. Fat Chance: Beating the Odds Against Sugar, Processed Foods, Obesity, and Disease by Robert H. Lustig

  3. Introductory Human Physiology, Duke University. Open online course taught by Dr. Jennifer Carbrey and Dr. Emma Jakoi,

  4. Nutrition for Runners with Dr. Mark Cucuzzella, Marathon Training Academy Podcast,

  5. How I Beat My Sugar Addiction, Carrots n Cakes Blog,

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