Re: Robert Lustig: The no candy man
A word we all learn when studying physiology is homeostasis. Serum electrolytes, plasma osmolarity and body temperature for example remain remarkably stable in the face of significant fluctuations in fluid and salt intake, and ambient temperature change. So why, despite mounting evidence to the contrary, do we suppose that weight and body fat would not normally be under homeostatic regulation too?
The answer appears to be that simplistic misapplication of the laws of thermodynamics supports the modern paradigm that weight and adiposity are singularly the result of energy imbalance (too much in and/or too little out). Another way of looking at the problem of obesity, and its associated diseases, are that they result from a derangement of normal homeostatic mechanisms; obesity does not cause Type 2 Diabetes (say), but is merely associated with it. Something else may actually be causing both.
The essay by Gary Taubes (1) and the profile piece on Robert Lustig and his work (2), and the recent review of Yudkin’s book on the perils of sugar (3) published in the journal are therefore most welcome contributions to the debate. In particular the hypothesis they all appear to support is the notion that the underlying abnormality linking both obesity and the various manifestations of the Metabolic Syndrome (e.g. type 2 diabetes, ischaemic heart disease, fatty liver, polycystic ovary syndrome) is excessive insulin secretion.
Insulin is the hormone of storage. It converts glucose to glycerol and facilitates its uptake into, and blocks release from, adipocytes. Insulin is mainly evoked by post-prandial glycaemic surges; low-carbohydrate meals barely alter plasma glucose levels, where as highly glycaemic meals cause large and sustained rises in glucose. Our modern highly processed and abnormal high glycaemic loaded diets evoke supra-physiological surges in insulin to contain these waves of glycaemia. It would appear that excessive and persistent hyperinsulinaemia, and the resultant insulin resistance that often follows in its wake, is the natural result of our unnatural diets; homeostasis gets overwhelmed.
I therefore propose two hypotheses for consideration; firstly that insulin is not, as we have been taught, the body’s natural response to insulin, but rather its last defence, and secondly that the excessive domination of metabolism by insulin, so characteristic of modern lifestyles, is the root cause of much of our chronic ill health and disease today. It would appear that the weight loss and improved blood chemistry that follows cutting out highly glycaemic carbohydrates is more about with working with biology, than about the laws of physics.
GP, Saxmundham, UK.
Competeing Insterests: none
1 The science of obesity: what do we really know about what makes us fat? Taubes G. BMJ 2013;346:f1050
2 The no candy man. Ravichandran B. BMJ 2013;346:f2287
3 Sugar and the heart: old ideas revisited. Watts G. BMJ 2013;346:e7800
Competing interests: No competing interests