Three Reasons Why Sugar May Make Us Ill

I was asked recently by a reader for three good reasons why sugar is bad for us; specifically, I was asked “Can you give me links to 3 studies which definitely prove in a reductionist way, that sugar makes us ill?” My reader is a well-educated German gentleman who, I believe, wants links to respected peer-reviewed studies which demonstrate that high levels of sugar consumption can have negative health effects.

Here, we are not talking about the natural sugar content of fruit, since, in this form, we saw in the previous blog 1 that the sugar naturally bound to fruit has a positive effect on health. Neither will we be looking at artificial sweeteners, since we already covered in a previous blog 2 how they are not a wise alternative to sugar. Rather, we’ll only look at three studies which specifically discuss refined sugar the likes of sucrose (table sugar), fructose and high fructose corn syrup. This is where the sugar has been separated from the plant in which it grew, and separated from its natural form, where it was bound to the natural fibre and other macro- and micro-nutrients therein.

Now, it may come as a bit of a surprise to some, but there’s no universal scientific agreement on the conventional assumption that eating sugar causes obesity or diabetes. This is based on the assumption that sugar will turn to fat  within the body – a process called de novo lipogenesis. However, respected research has shown 3 4 5 that this conversion of sugar to fat only happens when sugar is consumed in high quantities. Indeed, even in a study 6  where test subjects were given an extra 135 grams of refined sugar daily (that’s around 35 teaspoons or over 500 extra calories), the subjects only produce 4 grams (36 calories) of extra body fat per day. The latter study conclusion was that: “De novo lipogenesis increases after overfeeding with glucose and sucrose to the same extent in lean and obese women but does not contribute greatly to total fat balance.

So, whilst studies do show that long-term overfeeding of sugar can lead to an increase in body fat, and thus contribute to the development of obesity, diabetes etc, it is not going to do this in small quantities.  An explanation of the cause of the world-wide tsunami in obesity and other weight-related diseases is to be found elsewhere – probably in the amount of animal fats consumed in the SAD (Standard American Diet). As Dr McDougall has been saying for decades 7 , “The fat you eat is the fat you wear.

The process involved here is quite simple – our body’s cells become filled with fat and the receptors that normally respond to a high level of blood sugar become ‘blocked’ and thus unable to remove excess sugar from the blood – resulting in insulin resistance. This can then result in the development of diabetes and other associated diseases. The fact that feeding high-fat foods (rather than high-sugar foods) causes high blood sugar levels is not only supported these days by the likes of Dr Greger 8 was demonstrated in studies 9 dating back almost a century!

Problem. What problem?

So, where’s the problem with refined sugar? And what are the three links my German friend requested?

1. Sugar and muscle mass as we age

A 2007 study 10 found that participants aged 60 and above who consumed at least 36 grams of  refined sugar a day (about the amount in a can of Coke) had more than double the risk of becoming frail over the follow-up period compared to those who consumed less than 15 g per day. The reason for this may be related to sugar’s impact on muscle mass, since other research 11  has found that high sugar intake (particularly in processed foods) may diminish the body’s ability to maintain muscle mass with age. Eating whole fruit, which can contain high levels of sugar, does not have this negative result.

2. Sugar and depression

A 2017 study 12 confirmed earlier studies 13 14 15 that all suggest a strong link between high refined sugar consumption and depression (in this case, particularly in men).  Men who consumed 67 grams or more of sugar per day were 23% more likely to be diagnosed with depression in a five-year period than men who ate 40 grams or less. The researchers conclude: “…our findings indicate that policies promoting the reduction of sugar intake could additionally support primary and secondary prevention of depression.

3. Sugar and heart disease

A 2014 study 16 found an association between a high-sugar diet and a greater risk of dying from heart disease. The lead researcher, Dr Hu, commented 17  that “Basically, the higher the intake of added sugar, the higher the risk for heart disease.”

The mechanisms involved may be:

  • sugar-overload of the liver
    • resulting in a greater accumulation of fat, which may turn into fatty liver disease, a contributor to diabetes, which raises the risk of heart disease
  • rise in blood pressure
    • known to be a pathological pathway to heart disease
  • increase in chronic inflammation
    • also a known pathway to heart disease

Dr Hu concludes that: “The effects of added sugar intake — higher blood pressure, inflammation, weight gain, diabetes, and fatty liver disease — are all linked to an increased risk for heart attack and stroke.

Final thoughts

The latter study refers to weight gain, although I earlier argued that it’s the fat in the diet and not the sugar that seems to be the major reason for weight gain (and thus, the associated risks of diabetes etc). However, one important effect of refined sugar consumption mentioned by Dr Hu, but which I have not been able to cover within the three ‘reasons’ or ‘links’ provided for my German friend, is the “appetite-tricking” effect that refined sugar has on the body’s natural appetite-control system. Basically, the body doesn’t realise it’s consumed so much when the calories taken in are from refined sugars. Hence, it’s much easier for people who eat lots of sugar (for instance in sugary beverages or in confectionery, biscuits, pastries, etc) to add more calories to their regular diet.

We have also not covered the effects that sugar has on dental health, nor looked at the important issue of whether or not sugar is an addictive substance. Sugar is rarely eaten in isolation. I mean, you wouldn’t just sit down and spoon eight teaspoons of sugar into your mouth; but you would finish off a pack of chocolate biscuits which contain much more than eight teaspoons! You know where I’m coming from with this…

I hope this will satisfy my German friend’s request and suggest that refined sugar intake, whilst not as strongly linked to the development of the likes of diabetes and obesity as many think, is not something that should be encouraged; indeed, if it’s consumed in high quantities over long periods of time, it is likely to make us ill.

Additionally, new research is always appearing which gives more substance to the importance of eating whole plant foods, rather than Frankenfoods (those ‘foods that have been commercially isolated from whole plants). I suspect that there will be additional discoveries in the future that support the hypothesis that any substance isolated from it original plant source is to be treated with caution – and this certainly refers to refined sugars.

The odd bit of added sugar won’t cause you any harm? Well, probably not, but for many people, sugar is habit-forming and getting used to living without it altogether can be much easier than trying to moderate its use.


  1. Am I Eating Too Much Fruit? []
  2. Bitter Effects of Artificial Sweeteners []
  3. Hellerstein MK. De novo lipogenesis in humans: metabolic and regulatory aspects. Eur J Clin Nutr. 1999 Apr;53 Suppl 1:S53-65. []
  4. Acheson KJ, Schutz Y, Bessard T, Anantharaman K, Flatt JP, Jequier E. Glycogen storage capacity and de novo lipogenesis during massive carbohydrate overfeeding in man. Am J Clin Nutr. 1988 Aug;48(2):240-7. []
  5. Minehira K, Bettschart V, Vidal H, Vega N, Di Vetta V, Rey V, Schneiter P, Tappy L. Effect of carbohydrate overfeeding on whole body and adipose tissue metabolism in humans Obes Res. 2003 Sep;11(9):1096-103. []
  6. McDevitt RM, Bott SJ, Harding M, Coward WA, Bluck LJ, Prentice AM. De novo lipogenesis during controlled overfeeding with sucrose or glucose in lean and obese women. Am J Clin Nutr. 2001 Dec;74(6):737-46 []
  7. Sugar, Coated with Myths. Dr McDougall Newsletter September 2006 []
  8. Fat is the Cause of Type 2 Diabetes. Written By Michael Greger M.D. FACLM on November 17th, 2016 []
  10. Barzilay JI, Blaum C, Moore T, et al. Insulin resistance and inflammation as precursors of frailty: the Cardiovascular Health Study. Arch Intern Med 2007, 167:635-641. []
  11. Cleasby ME, Jamieson PM, Atherton PJ. Insulin resistance and sarcopenia: mechanistic links between common co-morbidities. J Endocrinol 2016, 229:R67-81. []
  12. Nature. 27 July 2017. Sugar intake from sweet food and beverages, common mental disorder and depression: prospective findings from the Whitehall II study. Anika Knüppel, Martin J. Shipley, Clare H. Llewellyn & Eric J. Brunner. []
  13. El Ansari, W., Adetunji, H. & Oskrochi, R. Food and mental health: Relationship between food and perceived stress and depressive symptoms among university students in the United Kingdom. Cent. Eur. J. Public Health 22, 90–97 (2014). []
  14. Yu, B. et al. Soft drink consumption is associated with depressive symptoms among adults in China. Journal of Affective Disorders 172, 422–427 (2015). []
  15. Westover, A. N. & Marangell, L. B. A cross-national relationship between sugar consumption and major depression? Depression and Anxiety 16, 118–120 (2002). []
  16. JAMA Intern Med. 2014 Apr;174(4):516-24. doi: 10.1001/jamainternmed.2013.13563. Added sugar intake and cardiovascular diseases mortality among US adults. Yang Q, Zhang Z, Gregg EW, Flanders WD, Merritt R, Hu FB. []
  17. Harvard Men’s Health Watch. The sweet danger of sugar. Too much added sugar can be one of the greatest threats to cardiovascular disease. Here’s how to curb your sweet habit. Published: May, 2017 []