Terminology

Here is a list of the definitions we use in the article:

Satiety: how satiated you feel after a meal

Appetite: your desire to eat

Hunger: your need to eat

Craving: an intense desire to consume a specific food

Fullness: the feeling of being full || having eaten enough

Ad libitum: eating as much as you want until you are full

Does the ketogenic diet suppress appetite?

People spontaneously eat fewer calories on keto

People tend to eat fewer calories while on the ketogenic diet (Gibson et al., 2015; Aragon et al., 2017). This happens spontaneously, because they aren’t asked to restrict calories. Hence, this diet could fit you well if you dislike calorie counting.

“The efficacy of [Ketogenic Diets] is (...) often attributed to a suppression of appetite resulting in spontaneous decrease in energy intake”. - Gibson et al., 2015

In the graph below you can see how many calories subjects consumed. Across 11 studies, subjects ate, on average, 2,331 ± 473 kcal at baseline, and 1,694 ± 390 kcal on the ketogenic diet.

Remember, these are ad-libitum studies! The subjects were not asked to restrict calories (only carbs).

Figure by Sci-Fit. We pooled the average caloric intake of the ketogenic studies in our analysis, and calculated the standard deviations. Data is extracted from 11 ad libitum ketogenic studies.

That is the good news.

The bad news is that people eat more calories and carbs after a while on the diet. In other words, adherence to the diet drops. This happens across all types of diets and isn’t unique to keto. We will cover adherence in the next part of our keto series!

Does keto make you eat fewer calories than other diets?

Sadly, most studies compare carb restricted keto groups to calorie restricted control groups. We can’t compare them directly.

Still, we have some relevant studies:

Study Caloric intake Time of measurement Calorie restriction? Johnstone et al., 2008 Crossover Keto ~1732 kcal Moderate carb diet ~1899 kcal Week 4 No McAuley et al., 2005 RCT Atkins (keto) −~500 kcal Zone −~500 kcal Week 8 No Dansinger et al., 2005 RCT Atkins −193 kcal Ornish diet (low fat vegetarian) −554 kcal Week 4 No Gardner et al., 2007 RCT Atkins −507 kcal Ornish diet −442 kcal Week 8 No

Non-ketogenic studies:

Study Caloric intake Time of measurement Calorie restriction? Gardner et al., 2018 Low fat −633 kcal Low carb −642 kcal Week 12 No Weigle et al., 2005 High protein −441 kcal Week 12 No

Overall, the data on this specific question isn’t settled yet. We might do a full analysis in the future.

Read Scientific Quotes

“ketogenic diets have shown appetite-suppressing potential exemplified by spontaneous caloric intake reductions in subjects on ketogenic diets without purposeful caloric restriction” - Aragon et al., 2017 “The efficacy of [Ketogenic Diets] is (...) often attributed to a suppression of appetite resulting in spontaneous decrease in energy intake”. - Gibson et al., 2015 “ad libitum intake of low-carbohydrate food that is high in fat and protein produces a weight loss that is more rapid and pronounced than with a conventional low-fat diet. This weight loss is most dramatic after 3 and 6 months of low-carbohydrate diet, there being no difference after 12 months between a conventional low-fat diet and the low-carbohydrate diet. The main reason for weight loss is a suppressed appetite, both through the high-protein content of the diet and the ketogenic nature of the diet.” - Erlanson-Albertsson and Mei, 2005” “Volunteers consumed significantly (P = 0.020) more energy (0.7 MJ/d) when following the MC nonketogenic diet than when following the LC ketogenic diet (Table 2).” - Johnstone et al., 2008

People feel less hungry on keto

Hunger is often increased when dieting (MacLean et al., 2011; Gibson et al., 2015). Yet, that may not be the case for the ketogenic diet (Gibson et al., 2015). In almost all of the studies we analyzed, the ketogenic diet lead to a decrease in hunger.

This is quite unexpected, and very promising.

In a few studies (seen below), the scientists reported how hunger changed over time. For example, in Nymo et al, hunger increased at day 3 but slowly dropped thereafter. Yet, subjects in the other three studies dropped down and stayed at low hunger levels.

Figure by Sci-Fit. Each bar represents a point at which hunger was measured. All four studies used the Visual Analogue Scale for rating hunger. Read more about how scientists measure hunger (internal link).

A high protein diet makes you satiated

A large body of evidence demonstrates that protein is the most satiating macronutrient.

Why does this matter? Because the ketogenic diet is typically moderate or high in protein. This could be one explanation for why people eat fewer calories and feel less hungry on keto.

The average american diet is typically low to moderate in protein. It is difficult to quantify exactly what “low protein” means, because it is somewhat arbitrary. With that said, anything below 1 g protein per kg bodyweight can be considered low. Especially if your goal is to maintain or increase muscle mass.

Yet, it’s hard to say whether it’s ketosis or the high protein that causes people to eat fewer calories. For example, in Weigle et al., 2005 people ate −441 kcal per day when put on a high protein, normal carb diet. In McAuley et al., 2005, both the Zone group and the Atkins (keto) group ate ~−500 kcal after 8 weeks. This might be because both groups were high in protein. So in studies where the keto group ate more protein than the control diet, we would expect greater satiety for keto.

Exceptions to the rule:

“[the ketogenic diet] has demonstrated hunger-suppressive effects independent of protein content.” - Aragon et al., 2017

Protein intake wasn’t “high” in Nickols-Richardson et al., 2005 (94 g or 1.2 g/kg for keto), or in Foster et al., 1992 (70–90 g or ~0.7–0.9 g/kg). They still had a large decrease in hunger.

In Saslow et al., 2014 , the control group ate ~68 g or 0.7 g/kg protein and had the same reduction in hunger as the keto group (~106 g or 1.12 g/kg protein).

Protein was moderate in Johnstone et al., 2008 (123g or 1.2 g/kg for keto vs 135 g or 1.3 g/kg for control). If protein is the main reason for appetite suppression, why didn’t the control group reduce their hunger to the same extent as keto?

In studies where subjects eat Very Low Energy Diets (VLEDs), keto groups increase satiety and decrease hunger on 500-800 kcal and 50-60 g protein per day (i.e. Kovacs et al., 2004 ). If protein is so important, how come people feel so satiated on these types of diets ( Gibson et al., 2015 )?

These examples suggest that many factors affect satiety, beyond protein. We’ve covered some of the factors further down. [link to section].

Read more: a high protein diet does not prevent ketosis.

Read Scientific Quotes

“[the ketogenic diet] has demonstrated hunger-suppressive effects independent of protein content.” - Aragon et al., 2017 “An increase in dietary protein from 15% to 30% of energy at a constant carbohydrate intake produces a sustained decrease in ad libitum caloric intake that may be mediated by increased central nervous system leptin sensitivity and results in significant weight loss. This anorexic effect of protein may contribute to the weight loss produced by low-carbohydrate diets.” - Weigle et al., 2005 “We speculate that it is the protein, and not carbohydrate, content that is important in promoting short-term weight loss and that this effect is likely due to increased satiety caused by increased dietary protein. It has been suggested that the increased satiety might help persons to be more compliant with a hypocaloric diet and achieve greater weight loss.“ - Schoeller and Buchholz, 2005 “Weekly ratings of perceived hunger did not differ by diet group during the trial, which suggests, as discussed by others (31, 32), that it is the protein content of the diet and not the severity of dietary carbohydrate restriction that affects perceived hunger.” - Johnston et al., 2006 “Subjects in this group (i.e. keto) may have experienced greater satiety on a diet with liberal proportions of protein and fat.“ - Samaha et al., 2003 “This anorexic effect of protein may contribute to the weight loss produced by low-carbohydrate diets.” - Weigle et al., 2005 “...when reducing carbohydrate, a diet that reflects both a higher protein and a higher fat intake may be more effective in increasing satiety and resulting in a spontaneous calorie reduction than simply a high protein diet.” - Chatterton, 2015 “This study showed that individuals are significantly less hungry and exhibit significantly greater fullness/satiety while adhering to VLED compared with when they are in energy balance at baseline” - Gibson et al., 2015 “increased protein intake cannot explain why appetite is suppressed during VLEDs, which, while relatively high in protein, provide absolute protein intakes of only ∼ 50–60 g day –1 (which for obese persons is lower than the suggested normal intake of 0.8–1.2 g kg − 1 body weight per day [39]). Additionally, increased protein intake cannot explain the observation of an ‘absence of hunger’ during starvation or fasting regimes (35,61) – an observation that historically led to the initial development VLEDs to mimic this benefit (15). Further, well-controlled studies have shown that when protein intake is matched, a ketogenic high-protein diet suppresses appetite more so than a non- ketogenic high-protein diet in obese (20) and in lean subjects (62), highlighting ketosis as a plausible factor common to both VLEDs and KLCDs that could suppress appetite. Besides protein, another factor that could conceivably explain the effect of ketogenic diets on appetite is dietary fat (63). However, the contrasting low levels of dietary fat intake during VLEDs with the relatively higher levels consumed during KLCDs suggest that dietary fat intake is not a common factor explaining the appetite-suppressive effect of both diets.” - Gibson et al., 2015

Ketone bodies might suppress your appetite

Several studies mention that ketone bodies could suppress appetite (Jabbek et al., 2010; Veldhorst et al., 2012; Pesta and Samuel, 2014; Gibson et al., 2015; Karl et al., 2016). It is possible that ketone bodies accomplish this by altering hunger hormones (Sumithran et al., 2013; Stubbs et al, 2017). For example, Sumithran et al., 2013 reported correlations between hunger hormones and ketones.

Although, this doesn’t explain why subjects on moderate and high carb diets feel less hungry. This suggests that ketones might play a role in appetite suppression, but they’re not the sole reason. Researchers generally agree that this is a hypothesis (Brehm et al. 2005; Gibson et al., 2015).

There are some interesting studies out there, such as Stubbs et al., 2017. The subjects were given a ketone drink which reduced their hunger and desire to eat over 4 hours. Yet, we need to see more long-term data on this topic.

“The increased concentration of beta-hydroxybutyrate may act as an appetite suppressing substrate [62].” - Pesta and Samuel, 2014

Correlating carbs and hunger

We graphed hunger and carb intake to see if they correlate. In our analysis we excluded studies with more than 80 g of carbohydrates. We found a moderate linear correlation (Pearson’s R = 0.54) between hunger change and carb intake. If we assume that there is a connection between ketosis and hunger, then carbs might influence hunger on a ketogenic diet.

Figure by Sci-Fit. Note that we should interpret the correlation carefully. By itself, it does not suggest that fewer carbs = less hunger.

Read Scientific Quotes

Keto might affect cravings

Below, you see a graph of cravings. Every sphere represents a ketogenic diet group. The size of the sphere reflects how many subjects were in the study. For instance, the Foster et al., 1992 study had over 200 participants, so the sphere is much larger than the Rosen et al., 1982 study which had 8 participants.

There is a lot of variability in how keto affects cravings. There is data to suggest (not pictured) that those on a keto diet (Martin et al., 2011) have lower cravings for carbs or sweets compared to people on a low-fat diet.

Note that a craving is different from hunger. You can crave a specific food while feeling satiated, in general.

Figure by Sci-Fit. The cravings were measured using a 5-point scale. A drop in cravings by ~33% (as seen in Saslow et al., 2014) is notable, because they went from rarely feeling carb cravings to almost never feeling a craving. It’s hard to say what the practical implications of this is in the long-term