'Protect the liver, feed the gut…’ Dr. Robert Lustig takes fresh aim at processed food industry: ‘We’ve literally turned ourselves into foie gras’

By Elaine Watson

- Last updated on GMT

Dr Robert Lustig: "We need to protect the liver from the tsunami of refined carbohydrate and sugar that it has to deal with..."
Dr Robert Lustig: "We need to protect the liver from the tsunami of refined carbohydrate and sugar that it has to deal with..."

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One cigarette won’t kill you, observes pediatric neuroendocrinologist and sugar’s arch-nemesis Dr. Robert Lustig, but 10,000 cigarettes over 10 years just might. Processed food is also poisoning us, it’s just doing it much more slowly, contends Lustig, whose latest book boasts a characteristically provocative title: ‘Metabolical: The Lure and the Lies of Processed Food, Nutrition, and Modern Medicine.’

While many industry stakeholders balk at the term ‘processed’ food, arguing that ‘processing’ per se isn’t the problem, and that what matters is nutrient density, calories in, and calories out, Lustig says the evidence is only becoming more clear, that from a metabolic perspective, not all calories were created equal, and that “what we do to our food is the problem.”

While his emphasis on eating ‘real food' has echoes of Michael Pollen’s famous mantra, ‘Eat food, not too much, mostly plants,’ ​the devil is in the detail, says Lustig, who observes that Doritos, Coke, Cheetos, and apple juice are 100% plant-based, it’s what’s been done to the plants that turns them into junk food.  

Protect the liver, feed the gut

Take apples, he tells FoodNavigator-USA in a zoom call to discuss his new book​ for our upcoming weight management special edition. Discard the skin, and you remove much of the fiber and the flavonoids. Dry the apple and you lose most of the vitamin C. Pulverize it, filter it and pasteurize it to make juice, and what you’re left with might not be soda, but it’s pretty close.  

Throw the whole fruit (including the skin) into a blender to make a smoothie, and while you technically haven’t removed​ the insoluble fiber, he points out, you might as well have done: “The blades of the Vitamix, Breville, or Magic Bullet shear the insoluble fiber to smithereens, same as juice.

“As a result, the fiber can’t assemble the latticework for the gel in the duodenum, so it’s not protecting the liver from the onslaught of the sugar in the fruit smoothie.”

If you just ate the whole fruit as is, he said, the insoluble fiber would combine with the soluble fiber to form a gel that reduces the rate of absorption of sugars and slows the breakdown of starches. Reduced absorption means reduced transport to the liver, thus preventing the liver from turning excess energy into fat—in turn preventing liver insulin resistance. The fiber then makes its way to the large intestine, where it can become food for the gut bacteria.

'Fiber is perhaps the single most important nutrient for health, because it both protects the liver and feeds the gut'

Much the same applies to grains, he says. Most flour used in baking and other goods in the US is still white refined flour made from the starchy center of the wheat kernel (the endosperm). The germ, which contains the nucleic acids, polyphenols, flavonoids, vitamins, antioxidants, and other micronutrients; and the fibrous outer layer (bran), which contains soluble and insoluble fiber, are removed.

Whole grain flour is therefore a better option nutritionally, he says, although the way it is made on an industrial scale today - by separating out the three components (bran, germ, endosperm) using industrial roller mills and then reconstituting them - means that even though the flour contains the constituent parts in the same proportions as in the original intact grain​, it may not be metabolized in the same way.  

"If the endosperm stays within the geometry of the husk, you're going to get a low glycemic excursion and therefore, low insulin response, but if you've pulverized it and you've separated the three components, and then just add them back and call it whole grain, you're not going to get that. They say whole grain, but it's not actually whole or intact any more."

Lustig and Elaine
Dr Robert Lustig: "Our livers are stuffed from the sugar our bodies turn into fat; we’ve literally turned ourselves into foie gras..."

Inflammation and leaky gut

Lustig’s food philosophy – which may resonate more with biochemists than consumers, but is neatly encapsulated in the above whole apple vs apple juice example – can be summed up in six words, he says: ‘Protect the liver, feed the gut.’  

And the rest, he argues, is just window-dressing: “If you buy your organic, all-natural, GMO-free tortilla chips ​[or apple juice], at Whole Foods, you’re still stuffing your liver and starving your gut—you’re just paying more for the privilege.”

Today, he argues, “Our livers are stuffed from the sugar our bodies turn into fat; we’ve literally turned ourselves into foie gras. Our guts used to be full of beneficial intestinal bacteria that munched on fiber and kept everything in our bodies copacetic.

“Now, that food has been stripped of its fiber, and those bacteria get so hungry they eat the mucin barrier off our intestinal cells, setting us up for inflammation and leaky gut.”

A calorie is a calorie... except when it's not

It’s well-established, notes Lustig, that traditional methods for calculating calories have grossly miscalculated the metabolizable energy from whole nuts​. When you bite into a whole nut and break it up into smaller pieces, some of these fragments pass through your upper digestive system intact, and the energy they contain is not available; whereas if you pulverize them to make a nut butter, the gap between stated and actual metabolizable energy closes.

The food industry continues to espouse its mantra, a calorie is a calorie, that any calorie can be part of a balanced diet, so don't pick on our calories, go pick on somebody else's calories. But this is all based on Wilber Atwater's equation from 1916. If humans were bomb colorimeters that would be one thing, but we are not.”

Excess sugar?

When it comes to added sugar, which is in everything from ketchup and soda to hamburger buns and pasta sauce, we have to make big changes, he argues.

“We need to protect the liver from the tsunami of refined carbohydrate and sugar that it has to deal with because it's absorbed early in the intestine in the duodenum, where it goes straight via the portal vein to the liver, overwhelms the liver's capacity to be able to metabolize it, and you end up with liver fat and insulin resistance and chronic metabolic disease.”

But what about the argument – frequently cited by the soda industry – that sugar is not to blame for our health problems, because per capita consumption has actually been falling for the past 15 years,​ while rates of obesity, diabetes, and metabolic disease continue to rise?

“I don't argue that sugar consumption has fallen​,” says Lustig. “But we can only metabolize around 25 grams of added sugar per day, which is about 5% of total calories. But we’re not even close to 5% ​[according to the Dietary Guidelines for Americans​ we’re at about 13%, although Lustig argues the figure is higher], so here's my question:

“If you took triple the dose of arsenic that would kill you and you reduce it down to double the dose that would kill you. Would it still kill you?”

He also points to work by Alexander Bentley et al​ which points to a delayed impact of ‘excess sugar,’ noting that “the sharp rise in adult obesity after 1990 reflects the delayed effects of added sugar calories consumed among children of the 1970s and 1980s​,” from which you could extrapolate that more recent reductions​ in sugar consumption would not be expected to translate into a drop in obesity figures, yet. Read more HERE​.

“If you took triple the dose of arsenic that would kill you and you reduce it down to double the dose that would kill you. Would it still kill you?” Picture: Dr Robert Lustig

TOFI: Thin on the outside, fat on the inside

We’re also missing the point by focusing narrowly on obesity, insists Lustig, who says sugar causes health problems unrelated to its calories and unrelated to the attendant weight gain, and that obesity does not cause​​ metabolic dysfunction (cardiovascular disease, type two diabetes etc), but is a result ​​of metabolic dysfunction. 

Meanwhile, he argues, “When you look at the ‘normal weight’ population, approximately 40% also have metabolic syndrome—meaning they have metabolic dysfunction, insulin resistance, and high insulin levels. But for whatever reason, they’re just not obese.

“In some of them, their fat cells are insulin resistant, too, so energy doesn’t accumulate in the subcutaneous tissue. Instead they put it in other organs that shouldn’t have fat, such as muscle and the liver​ [TOFI, or thin on the outside, fat on the inside].”

Framing obesity debate as all about willpower and individual responsibility enables food companies to continue to sell cheap, nutritionally deficient products they know are contributing to metabolic disease, claims Lustig

So what do we do about all this?

When it comes to immediate threats, humans are remarkably good at responding to a crisis, he says. When it comes to complex, multifactorial problems that play out over a period of years, from climate change to obesity and metabolic disease, our track record is lousy, however.

And by framing structural, systemic, societal problems through a lens of individual freedom and responsibility (it’s your fault you’re fat, the government is coming for your Big Gulp), the food industry has been pretty successful at avoiding regulatory interventions, which given the scale of the crisis (almost one in ten Americans now has diabetes requiring some form of drug therapy, 45% of US adults have hypertension, 74% are overweight or obese) is no mean feat, he says.

We have to come up with a food business model that rewards manufacturers for doing the right thing. But currently, all the inducements are for doing the wrong thing​.”

So if he could wave a magic wand, says Lustig, “The one thing I would do immediately is get rid of food subsidies for corn, wheat, soy, sugar. We have subsidies for all these commodity crops and not for vegetables and fruit, and it distorted the market. What if you actually paid the food industry for quality instead of quantity?”

'Healthy’ and ‘natural…’ two words in food marketing that don't mean anything...'

As for educating consumers, it's important, but it hasn't really moved the needle, he observes (we have more information about food and nutrition at our fingertips than ever before, but we're still getting fatter and sicker).

One thing we do know is that Nutrition Facts labels and front of pack schemes such as Facts Up Front​ haven't transformed our eating habits, he says, “and to be honest with you I don't think they will, because, as I keep saying, it's not what's in the food, it’s what’s been done to the food, and the calories don't really matter. It's about whether those calories are accessible to the microbiome as opposed to your duodenum​.”

As for ‘healthy’ labels – the FDA is currently conducting research on​ ​symbols brands could use on a labels as a graphic representation of the nutrient content claim ‘healthy’ – Lustig is scathing.

“The FDA is totally off on this ​[the criteria for a ‘healthy’ nutrient content claim, which permits any amount of sugar, but specifics certain types of fat ratios, and requires the addition of one positive nutrient such as vitamin A or calcium] … I mean what kind of bullshit is this? 'Healthy’ and ‘natural…’ two words on food labels that don't mean anything.”

'Ultra-processed' foods?

If we’re going to deploy any front of pack labeling system, Lustig favors something like the NOVA system​ the brainchild of São Paulo public health nutritionist Carlos Monteiro, which divides food into four categories: 1) unprocessed (whole, untouched); 2) minimally processed (e.g., mechanical dispersal, removal of inedible or unwanted parts, fractioning, grinding, drying, fermentation, pasteurization, cooling, freezing); 3) moderately processed (e.g., removal of fiber and/or addition of salt, sugar, oil, or preservatives); and 4) ultra-processed (unusual combinations of multiple components, flavor enhancers, dyes, binders, additives).  

It's not perfect he says, “But it’s category four, the ultra-processed category, in which fiber has been removed, sugar added, and micronutrients are deficient, that provides the strongest correlation with chronic disease​.”

Non caloric high intensity sweeteners

So if excess amounts of added sugar are screwing up our metabolism, what should we replace it with?

In an ideal world, says Lustig, we’d just switch to a whole food diet packed with fruits, veggies, whole grains, unprocessed meat, fish and so on, but in reality, the packaged food industry is going to try and find ways to give us the processed foods we are accustomed to (ketchup, soda, cookies) where sucrose is replaced by stevia, or aspartame, or combinations of these with bulk sweeteners such as allulose, or erythritol, or maltitol.

Some new bulk sweeteners seem quite promising, although more research is needed, claims Lustig.

However, “diet​ [high intensity, non caloric] sweetener consumption is also correlated with metabolic syndrome​,” he argues, although he acknowledges that there is no proven causal link (proponents of diet sweeteners, meanwhile, argue that people with metabolic syndrome simply consume more diet drinks because they are watching their sugar/calorie intake).

So what’s the potential concern about some high intensity sweeteners, which have been exhaustively tested by regulatory agencies across the world? “You drink a soda,” ​says Lustig. “The tongue sends a signal to the hypothalamus that says, ‘Hey, sugar is coming, get ready to metabolize it.’ The hypothalamus then sends a signal along the vagus nerve to the pancreas, saying, ‘A sugar load is coming, get ready to release the insulin.’”

If the sugar never comes because the soda is sweetened with, say, sucralose, your pancreas may still produce insulin​, he claims (although other studies have shown no effects of non-caloric sweeteners on insulin production): “The sweet taste alone can both stimulate appetite and insulin release, which drives energy storage.”

Fat cells have receptors for diet sweeteners on them, no one knows why

He also pointed to one recent in vitro study​ in which human adipocyte (fat) tissue-derived mesenchymal stromal cells were exposed to sucralose, which appeared to promote additional fat accumulation within cells, which researchers at George Washington University speculated may have resulted from increasing glucose entry into cells through increased activity of genes called glucose transporters.

This is an in invitro study in petri dishes - not a human study (the researchers note that their findings "require further corroborative studies in vivo​") - but if sucralose can get across the intestinal mucosa and into the bloodstream, what is the effect on fat cells, asks Lustig?

"Fat cells have receptors for diet sweeteners on them, no one knows why. They bind to receptors on the fat cells and activate the energy storage directly. So maybe you don't even need the insulin, the diet sweetener itself will do it.”

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