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the right chemistry: keto diets work, but is there a catch?
there is little doubt that cutting way back on carbs results in weight loss. but how does all that fat impact cardiovascular risk factors?
nov 6 2019
4 minute read
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no bread. no pasta. no cereals. no potatoes. no carrots. no rice. no fruits. no beer.
here we come! but fret not. although you may be dumping carbs, you can still gorge on fish, butter, eggs, high-fat cheese, whipped cream, coconut oil and meat to your heart’s delight! really, though, how delighted can your heart be with such an overload of dietary fat? and why are so many people so keen on relegating carbohydrates to the nutritional waste bin?
most “keto” regimen experimenters are trying to gain the upper hand in the proverbial battle of the bulge. however, there are also those who engage in these very low-carb-high-fat diets hoping for help with some neurological diseases, diabetes, acne and even cancer. then there are the folks who have heard that cutting carbs leads to improved brain performance.
first, let’s deal with weight loss. way back in 1864, william banting in a “letter on corpulence addressed to the public” suggested avoiding “any starchy or saccharine matter which tends to the disease of corpulence.” banting was no medical expert, he was a british undertaker with a girth that would probably have prevented him from fitting into one of his coffins. after 20 frustrating years of trying everything from turkish baths to starvation diets, he sought help from william harvey, a physician who had been following famed french physiologist claude bernard’s work on the metabolism of sugar. harvey advised banting to give up sugar, as well as bread, butter, milk, beer and potatoes with the result that the undertaker lost 46 pounds and 12 inches off his waist in just 38 weeks. it was basically banting’s diet that was resuscitated and popularized by robert atkins in the 1970s, and it is an extreme version of the atkins diet that is now promoted by dedicated keto worshippers.
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there is little doubt that cutting way back on carbs results in weight loss. the question is, why? the body’s main source of energy is glucose, generally supplied by starches and sugars in the diet. if consumption of these carbohydrates is drastically reduced, below about 50 grams a day, energy has to be derived from an alternate source. at first, the 65 or so grams of glucose the body needs per day are produced from amino acids, sourced from proteins. but this process itself has a high energy requirement, and furthermore, the body is not keen on using up proteins that are needed to maintain muscle integrity. fortunately, there is a backup system that can swing into action.
the liver begins to convert fats into “ketone bodies,” namely beta-hydroxybutyrate, acetoacetate and acetone. these are then shuttled into the mitochondria, the cells’ little energy factories, where they are used as fuel. at this point the body is said to be in “ketosis,” with excess ketones being excreted in the urine. some acetone finds its way into the lungs and is responsible for the characteristic sweet scent of “keto breath.”
the usual argument for the more efficient weight loss associated with extremely low carb diets as opposed to low fat diets is that they produce a metabolic advantage because a lot of calories are needed to convert proteins to glucose. not everyone agrees with this, though. some suggest that ketone bodies either have a direct appetite suppressant effect, or that they alter levels of ghrelin and leptin, the respective appetite stimulating and inhibiting hormones. then there are those who argue that ketogenic diets succeed for the simple reason that they lead to a lower calorie intake. while it may sound seductive that keto worshippers can eat as much steak and butter as they want, they actually end up consuming limited amounts, likely due to the greater satiety effect of protein.
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there are numerous studies published over the last 20 years that have compared low-fat diets to low-carb diets with the overall conclusion that the low-carb diets are more effective in terms of weight loss, at least in the short term. unfortunately, there are no long-term studies of keto diets.
now for the question of how all that fat impacts cardiovascular risk factors. as one would expect, ldl, the “bad cholesterol,” does go up, although the increase is mostly in the “large particle” sub fraction that is deemed to be less risky. triglycerides, a significant risk factor, actually decrease on a very-low-carbohydrate diet, as does the body’s own production of cholesterol. levels of hdl, the “good cholesterol,” increase. but again, the problem is that there are no studies of people who have followed a keto diet long enough to note whatever effect such a diet may have on heart disease.
a keto diet can lead to weight loss. but what else can it do? we’ll discuss that next week.
joe schwarcz is director of mcgill university’s office for science & society (mcgill.ca/oss). he hosts the dr. joe show on cjad radio 800 am every sunday from 3 to 4 p.m.
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