The height of the Atkins Diet may have come and gone, but our fear of carbs is still going strong. Paleo, gluten-free and Ideal Protein diets are all arguably spin-offs of the low-carb craze. One of the many reasons that low-carb diets are thought to be more effective for weight loss is that some of them put your body into a state of ketosis.
What is ketosis?
In many low-carb diet books, ketosis is described as our body’s “fat burning” mode. Normally, glucose is our body’s primary source of energy. However, if there isn’t enough carbohydrate in our diet or our body’s glycogen stores, the liver is forced to convert fats to ketone bodies for energy instead.
How can I tell if I’m in ketosis?
Physiologically, ketone levels in your blood and urine will be higher than normal, and many people who are in ketosis have a distinct “fruity breath” caused by the increased amount of acetone (the same stuff that’s in nail polish remover) in their bodies.
Most of today’s low-carb diets are not ketogenic. Research suggests that carbs need to be restricted to 50 grams per day, with some going as low as 20 g. In other words, grains, potatoes, legumes and fruit are definitely out of the question, and it doesn’t take a lot of vegetables to send you over the limit!
What’s so special about ketosis for weight loss?
Though the idea that ketosis turns your body into a fat-melting machine is very appealing, most of the evidence (and there isn’t a whole lot) for ketogenic diets have to do with its effect on appetite. A 2008 study where obese men were fed low-carbohydrate, ketogenic diets compared to medium-carbohydrate, non-ketogenic diets found that subjects felt less hungry on the ketogenic diet, and as a result, ate almost 300 calories less per day. In four weeks, those in the ketogenic group lost nearly 14 lb, compared to 9.5 lb in the non-ketogenic group.
Ketogenic diets are often higher in protein than what most people would eat, and studies have shown that protein is more satisfying than fat and carbs. Ketogenic diets may also affect our hormones in ways that lead to a decreased appetite. Additionally, it may take more energy for your body to turn fat and protein into ketones versus using carbohydrates, causing a slight increase in metabolism.
Some of the weight loss for people on ketogenic diets can also be associated with water loss--carbs are called carbohydrates for a reason; they need water for storage! When your glycogen stores are depleted, then obviously the water needed to keep up those stores gets loss too.
So… why isn’t everybody doing it?
It’s unknown what the potential health consequences could be of eating barely any carbohydrates for an extended period of time. The longest anyone has been on a ketogenic diet in a research setting has been 12 weeks. There are two studies that followed subjects for a year, but the ketogenic phases only lasted for 20 and 30-45 days, respectively. (Though I can only imagine what the social consequences of having nail polish remover breath would be!)
My concern is whether a ketosis is a realistic lifestyle choice. I often cite a recent meta-analysis comparing low-fat and low-carb diets that concluded that in the long-term, all diets lead to similar weight loss, as long as you stick to it! In the low-carb vs. medium-carb study I mentioned above, the study authors found that both diets were ranked similarly in terms of palatability, but cautioned that “in real life, dieters may, by default, adopt more limited diet choice” and that “were the study conducted over a longer time, palatability ratings may gradually decrease.”
Not only could a ketogenic diet get boring, it can also get expensive (and you’re going to be that person when you’re going out with your friends)! Getting virtually all your calories from meat is definitely harder on your wallet than getting to choose a variety of vegetables, fruit, grains and legumes.
Ketosis is not a magic fat-burning state, but can result in more weight loss than other diets because it can decrease your appetite and help you eat less. Is it realistic--or even safe?!--to stay in ketosis for the long-term? If not, you might find yourself back on the weight rollercoaster, waiting for the next new diet trend.