Hello, I hope you are doing very well!

Do you ever find ideas and the motivation to learn come when you are at your busiest? What are you learning, or wish you had the time to learn about this week? I'd love to hear from you. I have started consulting with a new metabolic health program, it's only requiring about 5-10 hrs per week extra at the moment, but it took a few days of frenetic juggling before a nicer and more granular routine emerged. I look forward to the day each week when I write to you. It means so much that you want to read and learn from my new Analyse experiment. The fact that you have said 'yes' pushes me to do better each week. Sincerely, it means so much. Thank you.

(Furthermore, if you joined Analyse these past few days, and would like to have the first issue from last week, reply here and I shall send it to you. It's early days! I'd love for you to have the first issue).

We'll continue with our analysis of the monosaccharide fuels. Last week, we introduced the structure and function of glucose and galactose. The focus for this week is fructose: still a monosaccharide but with a different structure. As you saw last week, fructose is unique within the monosaccharides, as it's a ketose (contains a ketone group, as opposed to an aldehyde group, which we noted for glucose and galactose).

Delibero: To weigh well and consider maturely

We humans eat fructose in abundance. If you eat fruit, foods and beverages made from fruit; if you enjoy honey or create elaborate juices at home, you are eating fructose. You also eat fructose if you use sugar (sucrose) for baking and cooking, or if you eat any food outside the home that contains sugar. The list is so endless, but I'll limit myself to a few: fresh fruit, cooked fruit, processed fruit, honey, some vegetables, any sugar used in baking, syrups, cordials, juices of any type, soft drinks, sweet milk-based drinks, ice creams, ice blocks, sweet alcoholic drinks, lollies, cakes, desserts, chocolates, biscuits, muesli bars, most commercial breakfast cereals, some yoghurts. It will either occur as fructose alone or within the disaccharide molecule, sucrose (sucrose = glucose + fructose).

No matter the foods and beverages we reach for, most humans eat and/or drink fructose: you, your patients, your friends, your family, your kids and your colleagues. The exception would be the most restrictive phase of a ketogenic diet (hence, not the majority of humans). Again, a healthy dose of delibero is needed when we study fructose. Let's 1) Analyse its structure 2) Analyse the essentiality of fructose and 3) Study the conditions where our body synthesises its own fructose (yes, that is possible... endogenous fructose, 'generated within' the body).

Structure = Function. Part 2, Fructose.

Last week, we revised the 3 simplest sugars: glucose, galactose and fructose. We will recall that fructose is unlike the other 2, because of its structure: fructose is a ketose or ketone sugar. It contains a ketone group. Glucose and galactose do not, they contain an aldehyde group (aldose or aldehyde sugar). Therefore, because of its structure, fructose has different chemical properties, different functions and is metabolised differently by our body.

Firstly, the structure of fructose makes it incredibly water-soluble. It can dissolve in minute quantities of water. Think of honey, luscious, smooth and an amazing humectant. In its pure form, fructose is incredibly sweet, hence why high fructose corn syrup was developed: SO sweet, does not crystalise easily, and is relatively inexpensive to extract from sugarcane, sugar beets and corn. Its structure and high water solubility make it ideal as a sweet ingredient in foods and beverages.

However, because fructose is a ketone sugar, its structure is unlike glucose and galactose. This is significant. It means that for us humans, it is metabolised differently. Therein lies a few problems.

Firstly, fructose requires no insulin. Neither the transportation nor metabolism of fructose requires any assistance from insulin. Once ingested, fructose is avidly taken up by our liver cells. If we eat glucose at the same time (like well-balanced whole-food carbohydrates in their natural state), we tend to have better absorption of fructose across the small intestine. In the absence of glucose, the absorption of fructose is reduced, and quite variable overall. For some humans, their capacity to absorb fructose is low enough to induce symptoms of diarrhoea and GIT distress (the so-called "fructose intolerance").

So, all the fructose we absorb is delivered directly to the liver. Essentially, fructose becomes 'trapped' in the liver, thanks to the enzyme, fructokinase. Because of this, our liver is exposed to much higher levels of fructose than other organs. In the context of one's diet, this can injure the liver (we will analyse NAFLD: Non-alcoholic fatty liver disease in a not-too-distant issue). We can access the energy stored within fructose, via a pathway known as fructolysis (you may not have covered this pathway in undergrad. biochem). Think of fructolysis (for fructose) as similar to glycolysis (for glucose and galactose). Fructolysis allows for the splitting of the fructose molecule into 2 intermediates of the glycolysis pathway (for the deep nerds: fructose splits into dihydroxyacetone -3-phosphate and glyceraldehyde, revealing the point where fructose enters glycolysis through a 'side door').

As we saw last week with glucose, the biochemistry of fructose reveals we must apply context when discussing this sugar with human health. Delibero! Healthy portions of fructose attained while eating well-balanced meals and wholefood carbohydrate are essential for our health, especially for our energy supply. For example: In our liver, fructose can be converted into lactate, and lactate is essential for replenishing our energy as ATP. Our liver can also convert fructose into glucose via gluconeogenesis (this helps us maintain healthy blood glucose levels in a fasted state). In the fed state, glucose from fructose can be stored as glycogen, and used for energy later. Fructose can also eventually be stored as lipids (fats).

Lastly, our body can synthesise its own fructose from glucose. This conversion occurs whenever our glucose levels are excessive, such as 1) Diabetes, pre-diabetes and insulin resistance 2) regular snaking/eating or drinking a bolus of high-sugar food or drink 3) an overall diet high in carbohydrates. The conversion of glucose to fructose is known as the polyol pathway. Again, it's another pathway you may not have covered in undergrad, or ever before! We will analyse the critical importance of the polyol pathway for human health next week.

I'll also quickly mention this: the metabolic economy of your liver is immense. If you have ever undertaken a "detox" and felt terrible, if you have tried fasting and feel worse for it, this reflects the adjustments your liver is making to its metabolic economy, via the metabolic pathways I have mentioned in the past 2 weeks, plus a few others. Metabolic flexibility of the liver can improve if we commit to new lifestyle practices, not fleeting 'quick fixes'. This reflects the next latin term I have been waiting to introduce in Analyse.

Nutricium or Diaita: Way of Living... Way of Life

It's where the words diet and nutrition come from. I love this.

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I'm so grateful you chose to read and learn from my work interests this week. Let me know your questions. I read them all, and do my best to incorporate these into future issues and lectures.

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Kind regards, and be well.

Annalies

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