I am so pleased to introduce Dr. William Lagakos who has accepted my request to write an article for my blog! He is an expert in obesity, inflammation, and insulin resistance. In this post, Bill will present the findings from three recent controlled trials focused on the effects of low-carbohydrate vs low-calorie diets on appetite and weight loss. Bill runs his own blog and has authored his best-selling book, The poor, misunderstood calorie, which is one of the best resources on human energy metabolism. As most of you who follow the ketogenic diet know, "calorie is not a calorie" but calories are not insignificant: caloric intake definitely plays a role in weight loss.
The regulation of appetite is a complicated thing, with many players and many, MANY moving parts. One of these parts is diet composition. That is, ‘what’ you eat impacts ‘how much food’ or ‘how many calories’ for which you’re hungry. One theory is that carbohydrates are a major driver; as restricting them is very effective at reducing appetite in obese populations.
In 2008, Westman and colleagues compared two diets of vastly different macronutrient compositions in a population of obese type 2 diabetic patients (Westman et al., 2008). Participants assigned to the first diet were instructed to limit their carbohydrate intake to fewer than 20 grams per day, but they could eat as much of whatever else they wanted (a ketogenic diet). Those assigned to the second diet were instructed to actively restrict food and fat intake by 500 kilocalories (calorie restricted diet, “CR”).
Prior to starting the study, calorie intake for participants in both groups was ~2128 kilocalories per day. After 24 weeks, calorie intake by those assigned to the ketogenic diet spontaneously declined by almost 600, or 30%. Calorie intake in the CR group declined by almost 800, ~40%, via monitoring, calorie counting, and actively restricting intake. Interestingly, despite undergoing a greater reduction in food intake, the CR group lost significantly less weight than the ketogenic group (24 vs. 15 pounds, or 10 vs. 7% of starting body weight). This may have been due to the ability of carbohydrate restriction to preserve energy expenditure to a greater degree than fat restriction, as demonstrated by Ebbeling and colleagues (Ebbeling et al., 2012).
Thus, reducing carbohydrate intake spontaneously decreased appetite and this was accompanied by accelerated weight loss.
Furthermore, 3 of the 29 participants (10%) in the CR group were able to reduce or eliminate their diabetic medications whereas 8 out of 21 ketogenic (38%) dieters were able to do so.
In 2010, Yancy and colleagues did a variation on this by comparing a ketogenic diet to a calorie restricted, low fat diet supplemented with the weight loss drug Orlistat (Yancy et al., 2010). Orlistat works by inhibiting fat absorption, leading to steatorrhea (fatty diarrhea) if dietary fat isn’t adequately restricted. After 48 weeks, dieters in both groups reduced calorie intake by approximately 30%. In this study, reducing dietary carbohydrates led to a spontaneous reduction in intake that matched what the participants were able to achieve by actively ‘counting calories’ and restricting food and fat intake. And interestingly, yet again, the ketogenic dieters lost slightly more weight (25 vs. 21 pounds).
Furthermore, Orlistat reduces fat absorption, so, similar to the Westman study (above), the energy deficit may have been greater in the low fat diet group, yet still, weight loss was greater in the ketogenic diet group (speculatively, due to the impact of carbohydrate restriction on energy expenditure mentioned above).
Lastly, the need for antidiabetic medications decreased for 81% of the ketogenic dieters and 68% of the Orlistat + low fat diet group.
In 2014, Saslow and colleagues compared a ‘moderate carbohydrate, calorie restricted (MCCR)’ to a ketogenic diet in diabetic patients for 3 months and showed similar results (Saslow et al., 2014). Those assigned to the ketogenic diet spontaneously reduced intake by ~700 kilocalories per day whereas those actively restricting fat and food intake achieved a slightly greater reduction, 800. However, similar to the findings of Westman (Exhibit A) and Yancy (Exhibit B), ketogenic dieters lost significantly more weight (12 vs. 6 pounds).
And similar to Westman’s findings, significantly more of the ketogenic dieters reduced or eliminated their anti-diabetic medications:
In all three of these studies, reducing carbohydrate intake led to a substantial, spontaneous reduction in appetite. In the studies by Westman and Saslow the reduction was not as great as in the low fat, calorie restricted groups, although weight loss was significantly greater. In the study by Yancy, the reductions in intake and changes in body weight were similar, although there may be an unfortunate reason why this study differed from the other two…
Orlistat blocks fat digestion thus reducing its absorption. This means that while both groups reduced calorie intake to a similar degree, those taking Orlistat were absorbing fewer calories. Therefore it’s possible that the energy deficit in this group was much greater than it appeared to be, and this is supported by the significantly increased incidence of bowel incontinence and diarrhea.
Collectively, these studies suggest that carbohydrate intake plays a strong role in the regulation of appetite. Selective reducing carbohydrate intake leads to spontaneous reductions in food intake that match what people are able to achieve by actively restricting total food, fat, and calorie intake. Further, if the low fat dieters were able to eat to satiety, or until no longer hungry, then they wouldn’t need to actively restrict food intake and count calories; this doesn’t happen. In other words, this means they’re still hungry.