The fruit sugar ‘fructose’ isn’t generally considered a food that’s best avoided. After all, it comes from fruit.
Yet a radical new theory, developed by Richard Johnson, Professor of Nephrology at the University of Colorado, explains how it can trigger various damaging changes in our metabolism that make us more likely to develop chronic conditions such as diabetes, obesity and Alzheimer’s. If doctors better understood this, it could transform the new emphasis on sickness prevention that the government is promising.
Professor Johnson has produced what is effectively a biochemical wiring diagram of the connections fructose turn on and off, that are making an increasing number of people sick (1). Fructose makes up half of white sugar and most of fructose corn syrup which is the main sweetener in fizzy drinks and ultra-processed foods as well as being the main sugar in fruit.
How fructose affects body and brain
For instance, the amount of fat stored in the liver increases driving fatty liver disease, while the cell’s mitochondria, which create the body and brain’s energy molecule ATP, become less productive and blood pressure goes up. The result is that you get fatter, with more brain fog and fatigue and feel less inclined to exercise. It is a major promoter of diabetes.
Meanwhile an anti-ageing process called autophagy, that would normally clear away used up and damaged mitochondria, the cell’s energy factories, to make room for new ones, is disabled. When fructose gets into the brain, it is one of the factors causing the brain to form the useless clumps of amyloid protein found in Alzheimer’s, which is the focus of new drug treatments.
How on earth does fructose carry out such a blitz on our bodies? Why would the body run a program that was potentially so lethal?
“It would be wrong to think of fructose as some sort of major toxin, although it becomes neurotoxic in excess,” says Professor Johnson. “Instead, its remarkable range of effects are part of an ancient set of biological programs, which we call the ‘Survival Switch’, that work to prepare animals for hibernation, storing supplies in preparation for times of famine.” This is why fat storage increases and energy drops off producing brain fog. The trouble is we never run out of food or fructose.
Eat your fruit, don’t drink it.
None of this means that we should avoid fruits, which contain only a small amount of fructose that comes with beneficial fibre that feeds our vital gut bacteria, plus various nutrients. Not so for fruit juice, devoid of fibre. A glass of orange juice is the equivalent of three oranges, but without the fibre. So, eat your fruit, don’t drink it.
But this does explain why too much blood glucose from regularly eating generous amounts of sugar-laden foods and carbohydrates, is so damaging. The liver turns the excess glucose into fructose with all its knock-on effects. Other foods that can accelerate fructose production are alcohol and salt.
This rise in fructose makes it all too easy to start piling on the pounds, regardless of how many calories you have cut or how much further you are running. It’s a connection that very few nutritionists or GPs are aware of.
How can you tell if you have too much fructose?
A sign of the widespread damage the Switch can cause is that low ATP shows up in the brains of people with disorders such as obesity, diabetes, fatty liver disease and Alzheimer’s. Understanding this points to new ways to cut the risks of these chronic disorders.
A simple, but very effective one, is to run a blood test – HbA1c – the gold standard test GPs use to screen for diabetes. A recent study of 374,021 older men with diabetes found that keeping the level of HbA1c stable over three years cut risk of dementia by a third (2). Similar benefits have been found with patients with pre-diabetes. But far lower levels of HbA1c than those used to diagnose diabetes are associated with the first signs of brain shrinkage, which is the hallmark of cognitive decline, even in teenagers.
That is why the UK Alzheimer’s prevention charity foodfothebrain.org, as part of its ‘citizen science’ research is testing blood levels of HbA1c on a home test kit to find out not only who is at risk, but also how to reverse that risk. The assessment includes a free test that calculates your future Dementia Risk Index and suggests various lifestyle and nutrition changes to help reduce it, including a low fructose diet – see www.foodforthebrain.org/fructose
What can you do?
Foodforthebrain.org recommendations, also include increasing omega-3 intake from oily fish, increasing B vitamins, especially B12, as well as an active lifestyle. In addition, the charity also promotes a low ‘glycaemic load’ (GL) diet, low in fructose, with periods of going ‘ketogenic’ by keeping sugar and carbohydrates to a minimum. The body responds by creating ketones, energy packets that can replace glucose as an energy source for the brain, helping to undo the damage.
‘Burning ketones can also increase the number and output of the cell’s energy factories, known as mitochondria, which are damaged by fructose,’ says Professor Robert Lustig of the University of California, author of the best-selling book Metabolical.
Both Professor Johnson and Professor Lustig are part of the foodforthebrain.org’s Alzheimer’s Prevention Expert Group and have written to UK dementia prevention authorities to add sugar, and specifically a high fructose diet, to the list of known risk factors (3).
This approach also naturally promotes the enzyme GLP-1, targeted by the weight loss drugs Ozempic and Wegovy, but without the side-effects or rebound weight gain.
Being fructed
Today’s typical diet of burgers, cola drinks, fruit juice, ice cream, bread, biscuits, cakes and confectionary, plus alcohol and salt, is a dementia time-bomb. Our brains are literally being ‘fructed’. We see the same shrinkage in the same regions of the brain in teenagers with a high sugar intake that are seen in Alzheimer’s (4). We think of the resulting dementia as type-3 diabetes.
To find out more, test your HbA1c and take part in the dementia prevention research visit www.foodforthebrain.org/fructose
References:
1. Johnson RJ et al. The fructose survival hypothesis for obesity. Philos Trans R Soc Lond B Biol Sci. 2023 Sep 11;378(1885):20220230. doi: 10.1098/rstb.2022.0230
2. Underwood PC et al HbA1cTime in Range and Dementia JAMA Netw Open. 2024 Aug 1;7(8):e2425354. doi: 10.1001/jamanetworkopen.2024.25354
3. https://foodforthebrain.org/lancet-commission-letters/
4. Yau PL et al Obesity and metabolic syndrome and structural brain impairments in adolescence. Pediatrics. 2012 Oct;130(4):e856-64. doi: 10.1542/peds.2012-0324
