Book Review: Salt, Sugar, Fat

Michael Moss is a Pulitzer prize-winning journalist who has made a career writing about the US food system.  In his latest book, Salt, Sugar, Fat: How the Food Giants Hooked Us, he attempts to explain how the processed food industry has been so successful at increasing its control over US "stomach share".  Although the book doesn't focus on the obesity epidemic, the relevance is obvious.  Salt, Sugar, Fat is required reading for anyone who wants to understand why obesity is becoming more common in the US and throughout the world.

The greatest strength of Salt, Sugar, Fat is its detailed insider perspective on the workings of the processed food industry.  Similar to Dr. David Kessler's book The End of Overeating, Moss interviewed a number of high-level current and former food industry executives, as well as industry and academic scientists, who were remarkably candid in explaining how the food industry gets people to buy its food.  He also dove deeply into historical records that explain how the processed food industry became the behemoth it is today.

In contrast to The End of Overeating, Moss places a greater emphasis on advertising and societal changes that have driven the demand for processed food, rather than focusing exclusively on the palatability/reward value of the food itself (and the cues that make us crave it).  The picture that emerges is that the processed food industry is an extremely sophisticated system that uses every tool in its tool belt (including quite a bit of science) to get you to purchase and consume its food.  Companies do what they can to exploit the hard-wired food selection systems in our brains.

Rather than demonizing the processed food industry, for most of the book Moss takes a fairly balanced view of its motives and actions (though he does demonize at certain times).  One of the most interesting and unexpected aspects of the book is the seemingly sincere efforts some processed food manufacturers have made to try to improve the public health impact of their products, including imposing limits on the salt, sugar, and fat content of their foods.  Nevertheless, as Moss relates, the free market dictates that these efforts typically fail or are eviscerated, because companies that impose constraints on their products are quickly out-competed by companies that don't.  Adding insult to injury, publicly traded companies are savaged by Wall street investors if they attempt to consider anything other than profit in their recipes and marketing.

Part 1: Sugar

Part 1 begins with an exploration of a phenomenon that we all intuitively recognize: people like sugar, and they seek it out.  To put that into scientific terms, sugar is palatable and rewarding.  As Moss explains in a chapter titled "exploiting the biology of the child", this is particularly true of children, who have a hard-wired preference for sugar from birth.

The title of chapter two is also particularly telling: "how do you get people to crave?"  This chapter is about the highly scientific efforts to determine the "bliss point" for combinations of sugar, flavorings, and other ingredients that maximize the enjoyment and "craveability" (reward value) of soda and other foods-- ultimately driving purchase and consumption behaviors.

The next few chapter launch into a fascinating history of the US cereal industry, from its modest roots with John Harvey Kellogg's unsweetened corn flakes, to his brother Will's betrayal by turning corn flakes into a sweetened cereal and ultimately founding Kellogg foods, to the modern cereal market in which some cereals are more than half sugar by weight.  

Also in this part comes one of Moss's scientific errors.  He states that the late Harvard physiologist Dr. Jean Mayer is "credited with discovering how the desire to eat is controlled by the amount of glucose in the blood and by the brain's hypothalamus, both of which are greatly influenced by sugar".  Dr. Mayer was a proponent of the "glucostatic hypothesis of appetite", in other words, that appetite is regulated primarily by blood glucose concentration (and/or glucose utilization), and that food intake subserves glucose homeostasis.  Although Dr. Mayer made a number of important contributions to the understanding of food intake and blood glucose regulation by the brain, many of which still stand today, the glucostatic hypothesis was largely discarded decades ago because it is too simplistic and it doesn't square with a number of basic observations (1).  Furthermore, I'm not sure what Moss meant when he wrote that blood glucose and the hypothalamus are "greatly influenced by sugar".  On a gram-for-gram basis, starch influences blood glucose more than sucrose, and as far as I know sugar itself has not been shown to have any special effects on the hypothalamus relative to other types of carbohydrate.

Part 2: Fat

This chapter begins with an interesting historical discussion of fat including Aristotle's view of it, followed by a small scientific error: Moss states that no taste receptor for fat has been found.  In fact, taste receptors for fat have been clearly identified in rodents, and emerging evidence is suggesting that the same may be true in humans (2, 3).  The research in humans is ongoing, but I would not state confidently at this point that no fat receptor has been found.

Part 2 touches on the neuroscience research that is used to exploit your hard-wired food selection behaviors.  This quote from Unilever scientist Dr. Francis McGlone was particularly telling:

There is not a lot to be gained from asking people why they like something, because they don't bloody know.  These are very low-level processes that drive these fundamental behaviors, and I'd gotten into [functional MRI brain] imaging because it's a good way to sort of bypass the mouth, if you like, so you can see just what neural processes are underpinning a behavior.

They are using fMRI to design ever more appealing foods, looking directly at the activation of reward/pleasure regions rather than relying on peoples' imprecise accounts of what they are feeling.  This is what consumers are up against.

In chapter 10, Moss assails the USDA for its alleged failure to effectively restrain the country's consumption of fat, and particularly saturated fat (even undermining its own nutrition guidelines by aggressively promoting cheese consumption).  I understand that opinions differ on the dietary fat and saturated fat issue, but Moss's perspective seems stuck in the 90s when he discusses the dangers of fat, cheese, and meats.  To be fair, I agree wholeheartedly that added fats and cheeses in processed foods can contribute to overeating and obesity, but I view the issue as more nuanced than the black-and-white picture Moss paints.  Moss's discussion of how we came to eat so much cheese in the US (hint: it's added liberally as an ingredient in processed foods) is very interesting.

Part 3: Salt

Salt is another palatability/reward factor that is used by processed food manufacturers to get people to purchase their food.  Without salt, many processed foods taste awful, with strong cardboard, metallic, and bitter flavors.  Chapter 12, "people love salt", contains a nice discussion of the reward value of salt, including reference to a paper titled "Salt Craving: the Psychobiology of Pathogenic Sodium Intake", which describes people who are literally addicted to salt (4):

Salt, the authors concluded, was similar in this way to "sex, voluntary exercise, fats, carbohydrates and chocolate, in its possessing addictive qualities".

Of course, most people are not literally addicted to salt, and never will be, but the fact that it can be addictive in some people emphasizes its significant reward value.  Its reward value is precisely why it is a ubiquitous additive in commercial food.

This chapter contained another scientific error, gleaned from the epidemiologist Dr. Eric Rimm, who allegedly said the following about potato chips:

"The starch is readily absorbed," he told me.  "More quickly even than a similar amount of sugar.  The starch, in turn, causes the glucose levels in the blood to spike, and this is a concern, in relation to obesity."

Really!  I don't mean to pick on Dr. Rimm specifically, because this idea is widely repeated, but it has no scientific basis.  First, potato chips have a relatively low glycemic load because they're mostly fat-- in other words, they don't spike blood glucose as much as an equivalent serving of plain potatoes or bread.  Second, increases in blood glucose if anything promote satiety, not hunger (5). Some would say that rapid glucose spikes are followed by dips, and that these dips promote hunger, but again although small post-meal dips are sometimes observed following the consumption of rapidly digested carbohydrate, these have not been convincingly linked to increased hunger or food intake.  Furthermore, these dips would be less likely to occur following potato chips than following an equivalent serving of plain potatoes or whole wheat bread, due to the smaller glycemic load of the chips.  Blood glucose spikes don't explain why potato chips favor overeating and fat gain.  People overeat potato chips because they're calorie-dense and they taste awesome.

Conclusions

Salt, Sugar, Fat is a very valuable book for anyone seeking to understand the current obesity and health crises in the affluent world.  The book's greatest strength is its in-depth insider account of how the processed food industry wins American stomach share by clever marketing, maximizing palatability/reward, and maximizing convenience.  The book's main weakness is Moss's brief but sometimes shaky scientific excursions.  Fortunately, these do not undermine the main thrust of the book.