Ketosis – an appetising solution for weight management?

The ketogenic diet (very low carbohydrate, high fat and protein) produces a 50% greater appetite suppressant effect compared to other very low calories weight loss diets. These results, which are achieved after three weeks of a ketogenic state are not different between men and women. Questions remain concerning the long term health effects of this diet on the gut microbiome and general health given the lack of fruit, vegetables and grains.

Australians currently spend $309.9 million annually on weight loss services, low-calorie weight loss foods and dietary supplements [1], and this figure isn't expected to slow down anytime soon with most people regaining the weight they’ve lost [2-4]. Maintaining diet-induced weight loss is physiologically challenging and brings with it compensatory responses on both sides of the energy balance equation [5] which are driven by interactions between the gut and brain. The result - an increase in hunger and reduction in fullness [6-8] combined with an overall reduction in energy expenditure [9-11]. If we take a deep dive into our physiology during diet induced weight loss we see an increase in ghrelin [12-14] (affectionately termed the ‘hunger hormone’) and a reduction in the concentration of several satiety hormones, such as peptide YY (PYY), glucagon-like peptide-1 (GLP-1) [12, 15-17] and cholecystokinin (CCK)[12,18]. But it might not be all doom and gloom when it comes to weight loss attempts according to Monash Nutrition’s Professor Helen Truby who has been researching weight loss and weight maintenance approaches for over 15 years. 

“We saw the rise of the very low carbohydrate diet popularised in the 1990’s by the Atkins Diet, and now the low carbohydrate approach is back, this time in the form of the ketogenic, or keto diet” commented Helen. Professor Truby explained that with this approach, an extremely low carbohydrate intake (20-40 g/day) must be followed and rigorously adhered to, with foods containing only protein and fat being permitted. This substantial shift in macro-nutrient ratio serves to strip the glycogen (carbohydrate) stores from the body, also taking with it water. Interesting fact - some of the initial weight loss observed on the scales is due to this water loss! “When glycogen stores have been depleted, the continued restriction of carbohydrate and subsequent lack of readily available glucose to use as a fuel source forces the body to utilise body fat and protein for energy. The end result - a state of ketosis.”

Because of their very low carbohydrate and high fat content, keto diets were initially demonised by nutrition professionals for being unbalanced - they lack fruit and vegetables and fibre in particular and have the potential to enable a very high proportion of energy to come from fat. “We haven’t even begun to understand the potential impacts on our gut microbiome, which is fed by prebiotics which are mostly plant and carbohydrate based in nature” explained Professor Truby. Longer term health effects aside, in short term studies (6 months) when ketotic diets are compared with other popular diets, there are few differences in weight loss achieved and little evidence of adverse effects [19].

While the idea of consuming a diet primarily consisting of protein and fat is unappealing to many, the keto diet is popular, with 11.8 million hits on Google and the hashtag #ketodiet being used 5.2 million times on Instagram. “One reason why inducing ketosis is a popular weight loss strategy is its appetite suppressant effect” commented Helen. Surely a great selling point for this weight loss method.

According to Professor Truby and her research team’s work which was published in the International Journal of Obesity, the appetite suppressant effect is not immediate but takes up to three weeks of being ketotic (if you can stick it out that long) before a measurable reduction in feeling hungry is achieved [20].

In their follow up study, which was recently published in the American Journal of Clinical Nutrition, the research team wanted to explore if males and females are different in how they respond to ketosis in terms of appetite and changes in the gut hormones controlling feelings of hunger and fullness. “Overall, gender did not influence objective measures of appetite (gut hormones) or how participants self-rated their feelings of hunger and fullness” commented Helen.

If people are considering using a ketogenic diet for weight loss, both males and females are likely to still experience feeling hungry - but this is about half of which you can expect for the same amount of weight loss if not in a ketotic state.

Professor Truby warns those about to embark on a ketogenic diet - “a further increase in the drive to eat can occur when ketosis has been reversed.” She reflected that “to date, we [healthcare professionals] have not done a good enough job at explaining to people when they lose weight what they should expect to feel in terms of changes in their appetite- each person needs to have effective strategies in place to help them manage and cope with ‘feeling hungry’. This is important in order to assist them in not overeating and regaining their lost weight”.

These studies highlight the substantial gap in our knowledge about how to help people manage those ‘hunger feelings’ and we need to know more about what helps people so we can share this with those who are trying to maintain a lower body weight.

Losing weight using keto diets is not suitable for everyone and should be done in collaboration and after discussion with a healthcare professional such as a GP or Accredited Practising Dietitian (APD). Click here to find an Accredited Practising Dietitian, or to learn about the Monash Nutrition clinic.

More information

This research was conducted in collaboration with Prof Catia Martins from the Obesity Research Group, Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Science, Norwegian University of Science and Technology Trondheim, Norway, where Professor Truby is an Honorary Professor.

Professor Helen Truby is an Advanced Accredited Practising Dietitian, a Fellow of the Association for Nutrition and is the Director of Dietetics in the Department of Nutrition, Dietetics and Food at Monash University. Her current research focuses on child and maternal health including weight management and optimising engagement and retention of health messages using social media. Click here to access Helen’s research profile. You can follow Helen on Twitter via @ProfTruby.

Stay up to date with the Monash University Department of Nutrition, Dietetics and Food on Twitter via @MonashNutrition.

Photo by Jez Timms on Unsplash

Publication information

Lyngstad A, Nemo S, Coutinho SR, Rehfeld JF, Truby H, Kulseng B, Martins C. Investigating the effect of sex and ketosis on weight loss-induced changes in appetite. Am J Clin Nutr. 2019;00:1-8

The American Journal of Clinical Nutrition is ranked 2 out of 124 Nutrition and Dietetics and has an impact factor of 6.549

Nymo S, Coutinho SR, Jorgensen J, Rehfeld JF, Truby H, Kulseng B, Martins C. Timeline of changes in appetite during weight loss with a ketogenic diet. Int J Obes (Lond). 2017;41(8):1224-31

The International Journal of Obesity is ranked 10 out of 124 in Nutrition and Dietetics and has an impact factor of 5.159

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