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A couple of years ago I saw a BBC Horizon television documentary about sugar and fat. One section mentioned three experiments performed by Dr Paul Kenny in which rats were given their ordinary rat food plus and unlimited supply of:

Experiment A. Unlimited sugar

Experiment B. Unlimited fat

Experiment C. Unlimited sugar and fat mixed together (50:50)

The stated results were that in experiment A the rats did not put on any weight, in experiment B the rats put on weight but not much and in experiment C they put on loads of weight and would eat the 50:50 mixture to the exclusion of their ordinary food. I also remember the documentary said the 50:50 ratio was critical and if the ratio was shifted too far in either direction then the weight gain effect reduced sharply. It was postulated that the reason for the satiety error was that sugar and fat don't often occur together in nature so the rats (and maybe people too) haven't evolved the biochemical feedback mechanisms for determining when they are satiated from such a mixture.

Edit: (Dr Kenny's work seems to be related to this earlier paper)

My question is this: have there been any follow-up experiments from this work? Either with humans, or perhaps with other unnatural mixtures like sugar/salt? or a triple-mix of sugar/fat/salt.

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    It would help to have some link to the original paper in the question. If you are talking about the study mentioned here: edition.cnn.com/2010/HEALTH/03/28/fatty.foods.brain , that's nature.com/neuro/journal/v13/n5/full/nn.2519.html but I can't access the full paper from here and it doesn't fit your details, as only one of the groups could feed ad libitum and there were no three different food mixtures. – YviDe Mar 7 '16 at 14:24
  • @YviDe - Also not sure how this relates to health? – JohnP Mar 7 '16 at 14:38
  • @YviDe: I don't know the original paper, but the link given in the top line of my question is a short video of Dr Kenny talking about his work. This paper is also related: ncbi.nlm.nih.gov/pubmed/2326345. – Mick Mar 7 '16 at 14:47
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    @JohnP: Excess bodyweight and ill-health are strongly linked. – Mick Mar 7 '16 at 14:48
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    I'm voting to close this question as off-topic because it's about rats and should be on biology or other site. – Graham Chiu Mar 14 '18 at 6:44