How too much carbohydrate damages your (beneficial) HDL cholesterol

| October 2, 2014

For anybody who has type 1 or type 2 diabetes, or who wants to avoid developing type 2, keeping to a low-carbohydrate, low glycaemic load (low GL) diet needs to be the front line treatment approach. This has been my advice on The Real Diabetes Truth all along and, as I reported here, it was recently backed up by a major review from an international team of specialists. Now, a new study adds further evidence that a low-carb diet is more effective than a low-fat one for weight loss and is also better for reducing cardiovascular risk factors.

And another good reason to keep to a low GL diet has emerged from other new research. It appears that a by-product from the breakdown of glucose in the body damages HDL cholesterol (that’s the ‘good’ kind that protects against heart disease). Along with the other negative effects of too much glucose, this explains why diets that are higher in sugars and simple carbohydrates can lead to increased cardiovascular risks.

In a head-to-head trial, people following a low-carb diet lost an average of 5.7kg in three months, while those on a low-fat diet lost less than half as much – just 2.6kg. What’s more, this initial weight loss was better maintained in the low-carb group, who still had an average loss of 5.3kg after one year, by which time the weight loss in the low-fat group had dropped back to 1.8kg.

When they looked at cardiovascular risk factors, the researchers found that, compared with the low-fat diet group, participants following the low-carb diet had more favourable changes in their blood levels of triglycerides and high-density lipoprotein cholesterol (HDL cholesterol). HDL is the ‘good’ kind of cholesterol that removes the ‘bad’ LDL kind from your arteries, so it is great to know that a low-carb diet boosts your levels of this heart-protective substance.

A high-carb diet, on the other hand, could seriously damage your HDL cholesterol. A study at the University of Warwick has found that methylglyoxal, a compound formed from the metabolism of glucose in the body, causes a chemical change in HDL that means it no longer works properly.2 So, the sequence goes like this: rapidly-processed carbohydrates like pasta or potatoes raise your levels of glucose, which means more methylglyoxal is formed, leading to lower levels of functional HDL cholesterol, which in turn means higher levels of damaging LDL cholesterol and a higher risk of cardiovascular disease.

If you have diabetes, you don’t only need to keep your blood sugar levels within the right range, you need to avoid swamping your body tissues with glucose, too. Apart from being converted to fat, too much glucose has many toxic effects in your body. To mention but a few of these, it produces damaging free radicals, cripples your immune system, accelerates ageing and drives the development of diabetic complications.

Sugar and high-fructose corn syrup destroy your health in multiple ways

Those rapidly-processed carbohydrates I mentioned are bad because they quickly turn into glucose. But sugar and high-fructose corn syrup (HFCS) are even worse, because along with glucose they also contain a lot of fructose, which behaves very differently (but just as badly) when you eat it.

Fructose doesn’t get transferred into your muscle cells for energy production the way glucose does. Instead, it goes straight to your liver, where it is converted to fat. Too much of it and you’re at high risk of a dangerous condition called non-alcoholic fatty liver disease. Here are a few other things to remember about sugar and HFCS:

  • They are high in calories but contain no essential nutrients (‘empty calories’)
  • They are as addictive as cocaine, since they trigger release of the ‘pleasure chemical’ dopamine in the brain
  • They may contribute to the development of cancer
  • They are the component of your diet, not the fat you eat, that puts you at increased risk of heart disease
  • Fructose doesn’t switch off the brain’s hunger signals the way glucose does, so is more likely to lead to obesity

Foods and drinks containing artificial sweeteners are marketed as a healthier option to sugar and HFCS for people who have (or who want to avoid) diabetes or metabolic syndrome. But as I wrote earlier here, they are actually very bad news. Recent research shows that artificial sweeteners cause the very conditions they claim to prevent by triggering our gut bacteria to produce damaging metabolic changes. I shall tell you more about this in my next blog post.

Wishing you the best of health,

Martin Hum
PhD DHD Nutritionist
for Real Diabetes Truth

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Bear in mind we are not addressing anyone’s personal situation and you should rely on this for informational purposes only. Please consult with your own physician before acting on any recommendations contained herein.


  1. Bazzano LA, Hu T, Reynolds K, Yao L, Bunol C, Liu Y, Chen CS, Klag MJ, Whelton PK, He J. Effects of low-carbohydrate and low-fat diets. Ann Intern Med. 2014; 161 (5):309-318.
  2. Godfrey L, Yamada-Fowler N, Smith J, Thornalley PJ, Rabbani N. Arginine-directed glycation and decreased HDL plasma concentration and functionality. Nutr Diabetes. 2014; 4(9):e134.
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Category: Diabetes and Heart Disease

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