By vegan naturopath Robyn Chuter.
Back when I was a naturopathy student in the early 1990s, no one I was acquainted with would have taken this question seriously. At that time, everybody ‘knew’ that being overweight was due to eating too much fat. End of story.
But then the Atkins diet – which exonerates fat, and vilifies carbohydrates as the culprit in weight gain – was reborn as the best-selling book Dr Atkins’ New Diet Revolution (having died a rapid death in its first incarnation as Dr Atkins’ Diet Revolution in the early 1970s).
A wave of me-too books followed: The Zone Diet, The South Beach Diet, Protein Power and a swag of others of lesser repute.
The Paleo diet craze also took off around this time, having originally been launched in the late 1970s.
While the proponents of each type of diet varied on some details, they all sang from the same hymn sheet on one point: ‘carbs’ (carbohydrate-rich foods) were bad. Carbs raised insulin levels, carbs turned to fat, carbs caused diabetes, carbs caused your arteries to block up, carbs caused inflammation, and so on ad nauseum.
Fast forward to 2016, and I’m still being told by clients on their first visit to me, that they’ve been restricting their fruit intake because their personal trainer, or some book they read, or a blog they follow, told them that “fruit is full of sugar” and “fruit makes you fat”.
I used to simply dismiss this preposterous claim with a rhetorical question: “Have you ever seen a fat monkey?” but the notion that fruit is fattening has wormed its way so deeply into the collective unconscious that I now need to address it more comprehensively in order to loosen its grip on my clients’ minds.
So this is what I tell them:
Firstly, epidemiological (population-based) studies have found that fruit consumption protects against weight gain – but fruit juice has the opposite effect (1).
Secondly, diets with a moderate amount of naturally-occurring fructose from fruit give better weight loss results than fructose-restricted diets (2).
Thirdly, the vilification of fruit by low-carb proponents is based on several misunderstandings about the fructose that fruit contains. Fructose is a simple sugar – called a ‘monosaccharide’ – that together with glucose, comprises sucrose, or table sugar.
Whereas glucose stimulates your pancreas to release insulin, allowing your cells to take up glucose and burn it for energy, fructose does not stimulate insulin secretion and is instead is taken up almost entirely by the liver.
Under certain circumstances, fructose can be turned into fat, which can either accumulate in the liver causing fatty liver and hepatic insulin resistance; or be sent out into the blood stream, causing systemic insulin resistance, high triglycerides and fat accumulation in adipose tissue.
Sounds scary, right? But what are those ‘certain circumstances’ in which fructose creates such calamities? Quite simply, experimental feeding trials in which obese individuals are fed fructose at levels that no normal human being would consume – typically 50% above the 95th percentile of consumption, or in other words, half as much again as is consumed by those who eat the most fructose in their regular daily diet (3)!
In trials where fructose has simply been substituted for the glucose normally consumed in the average human diet, there were no adverse effects on body weight, blood pressure, blood fats or insulin level; and in fact a possible benefit was found for glucose tolerance and glycemic control in diabetics (4).
The other point to bear in mind here is that fructose in the human diet almost always occurs in combination with glucose, whether in fruit, honey, table sugar or high fructose corn syrup, so trials where fructose is consumed in isolation give very misleading results.
Just how much fructose does fruit contain, anyway? Different fruits have different amounts, but as a rough guide, a 420 kj serving of fruit (say, 1 apple or 1 cup of blueberries) contains 10 g of fructose.
How much fructose was found to wreak metabolic havoc and cause weight gain in experimental feeding trials? 104 to 250 g per day, or an additional 18% to 97% of total daily energy intake (4).
So if you’re intending to eat 20 apples today, you probably need to back off on your fruit consumption (and yes, that IS a warning for people following Raw Till 4 and other diet plans based on fruit; apart from anything else, excessive fruit consumption nudges out vegetables, which should really be the basis of our diet for optimal health). Otherwise, relax and enjoy some of Mother Nature’s dessert, guilt-free!
(And if you’re looking for something a bit fancier than an apple, try this recipe: Black Sapote Mousse :).)