Carbohydrates: Digestion, weight loss, and function

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How are carbohydrates digested?

Have you read the article on what carbs are? It may be worth reading it first before you read this one as it explains what carbs are, the complex and the simple carbs. you can find the article here.

Both simple and complex carbs primary function is to provide energy for your body. The digestion process begins mouth when we chew and bite the carbs, our saliva releases enzymes amylase and ptyalin to break the polysaccharides into smaller chains called oligosaccharides, then into disaccharides, and finally our small intestine will break the carbs down into monosaccharides. This is the form in which our body can absorb the carbs.

When you consume carbohydrates, your blood sugar levels increase. Your sugar level can become too high, so it can be toxic to your blood vessels. If this occurs, the pancreas releases a hormone called insulin which transports and delivers the consumed sugars through the blood into muscles, fats and the liver. This process lowers the blood sugar as it stores the glucose in the muscles and tissues. If your sugar levels happen to become too low however, you can experience symptoms including: nausea, and fainting, and in extreme cases even death.

How does blood sugar increase?

Hormones glucagon and cortisol act to increase the blood sugar levels by secreting the glucose from the muscles and tissues back into your bloodstream. This process occurs when your blood glucose levels fall below homeostasis, which helps to maintain functional levels. 

How does insulin affect weight loss?

Insulin has received some bad press over the past years as it increases glucose (blood sugar), amino acid and lipid (fats) uptake into tissues like muscle and body fat. Moreover, insulin also inhibits lipolysis which is the first stage of fat burning. Lipolysis occurs when triglyceride (type of fat) within body fat are broken down and released into the body as free fatty acids. Insulin also inhibits fat oxidation and spares glucose for oxidation instead. You could call this the second stage of fat burning. Fat oxidation is breathing out of those free fatty acids that were previously released.

To clarify, when you are consuming high carbohydrate and low fat foods, insulin will inhibit lipolysis and fat oxidation (fat burning stages) and increase carbohydrate oxidation (burn simple sugars instead). On the other side, if you are consuming high fat and low carbohydrates, your insulin levels will be low in which case lipolysis and oxidation will increase to spare glucose. Whereas, if you consume moderate amount of carbohydrates and fats then you will burn roughly equal amounts of fat and carbohydrates (Norton and Baker, 2019).

Below you can watch a video explaining exactly WHY people say that carbs make you fat.

What is the Carbohydrate-Insulin-Model of Obesity (CIM)?

 According to this model, insulin has great effects on our metabolism. This model argues that insulin reduces lipolysis and fat oxidation (fat burning) and increases lipogenesis and fat transport into our body fat.  CIM argues that insulin traps fats inside the body fat tissues and creates a hormonal imbalance. This hormonal imbalance causes hunger which may cause over consumption. Since the fats are trapped within the fat tissue, they are unable to be transported around the other parts of the body. 

There was a meta-analysis (study of studies) conducted by Kevin D and Juen Guo (2017) who looked at Low Carb High Fat (LCHF) diets vs High Carb Low Fat (HCLF) diets. The results have shown that HCLF diets provided participants with a little more advantage in energy expenditure (calories out), enabling them to burn an extra 26 calories per day compared to LCHF. Furthermore, the results showed an increase in fat loss, approximately 16 grams of more fat loss per day compared to LCHF. Furthermore, opposing evidence against CIM emerged.

The experiment involved drugs which inhibited lipolysis, this drug was called Liraglutide which increases insulin levels. The study results showed neither fat gain nor increase in hunger occurred. Therefore, if insulin was the main driver of fat gain then this drug should have caused weight gain in participants and instead it caused weight loss.  

What is the Glycaemic Index. 

The Glycaemic Index (GI) is a method of classification which ranks carbohydrates on how quickly they are digested and absorbed by the body and how they affect our blood sugar levels. Essentially, the GI value of a carbohydrate ranks how quickly we can see sugar in the bloodstream after eating that carbohydrate. So the foods are given a number according to their effect on blood glucose levels with 100 at the top; 1-55 (low); 56-69 (medium) ; and 70-100 (high).  Carbohydrates which are easily digestible will create a rapid increase in the blood sugar levels. These will have a high GI value. Low GI does not mean that the carbohydrate is healthier, check the nutritional facts too. So to conclude on GI, it is a method which looks at how fast the carbohydrates enter into blood stream, how high the blood sugar goes and how long it stays for that high which both depend on quantity and quality of that carbohydrate.  

Recommended daily intake for carbohydrates

 The UK government recommends that  45% should come from starchy carbs and 5% can come from simple carbs.  

How to calculate carbohydrates?

Let’s take an example of a man whose total daily calories are 1600. Divide 1600 by 2 = 800 calories (1600/2=800).

To convert 800 calories into grams diving 800 by 4 = 200g (800/4=200). The reason why we divide by 4 is that there are 4 calories per 1 gram of carbohydrate.

You should consume carbs within 45 minutes of exercise.


Carbohydrates are fairly complex to understand but its important to know that these do not cause weight gain, everything is healthy in moderation. If you’ve enjoyed this content, please sign-up to our newsletter to be informed when the next articles will be released. Also, you an download 20 FREE nutrition and exercise tips as well as 6 fat loss recipes. Sign up below!


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Cho S, Dietrich M, Brown CJ, Clark CA, Block G. The effect of breakfast type on total daily energy intake and body mass index: results from the Third National Health and Nutrition Examination Survey (NHANES III). J Am Coll Nutr. 2003;22:296–302

Glycemic index, glycemic load, and chronic disease risk-a meta-analysis of observational studies Am J Clin Nutr (2008) 87(3): 627-637

Kevin, h. and Juen, G. (2019). Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition. [online] pubmed. Available at: [Accessed 17 Jul. 2019]. 

Norton, L. and Baker, P. (2019). Fat loss forever. 1st ed

Pi-Sunyer, X., Astrup, A., Fujioka, K., le Roux, C., Ortiz, R., Jensen, C. and Wilding, J. (2019). A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management | NEJM. [online] New England Journal of Medicine. Available at: [Accessed 17 Jul. 2019]. 

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