Think you know all about Keto Diet? A new study reveals your body’s first 24 hours on a ketogenic formula diet.
“Keto” is a shortened term for “ketogenic,” which describes the state of ketosis in the body. Ketosis occurs when the body utilizes fat as its primary fuel source instead of carbohydrates, providing us with quick energy when needed. Many people have regarded reducing carbohydrate intake as an efficient method to shed excess weight, particularly around the abdominal region.
A previous research study demonstrated that a 14-day Keto Diet (KD) resulted in spontaneous weight loss among individuals who were obese or had type 2 diabetes. However, various findings have emerged regarding the impact of a KD on total energy expenditure (TEE) and appetite perception.
In light of these contradictory results, a recent study published in Clinical Nutrition ESPEN aimed to compare the effects of a one-day ketogenic diet, fasting, and supplementation with ketone salts (KS) in contrast to a typical carbohydrate (CHO) diet on energy expenditure and appetite perception in healthy individuals.
Despite its numerous health benefits, such as reducing glycemia and insulin levels, the ketogenic diet (KD) has been associated with some negative effects, including an increase in low-density lipoprotein cholesterol. Moreover, long-term adherence to the KD can be challenging due to limited food choices and potential gastrointestinal problems. As a result, intermittent fasting and short-term diets have gained significant popularity in recent times.
Full fasting has been found to decrease energy expenditure (EE) and increase appetite. Therefore, adopting a 24-hour ketogenic diet could be an effective strategy for weight reduction. Currently, exogenous ketones (EXO) are available commercially as racemic ketone salts (KS, D/L-BHB) or ketone esters (KE, D-BHB), which can be used as supplements to achieve ketosis.
The effects of exogenous ketone supplementation on appetite suppression have yielded mixed results. Some studies indicate that KE can mimic the appetite suppressant effect of a ketogenic diet by reducing ghrelin levels. However, other studies have contradicted these findings, suggesting that oral consumption or intravenous administration of KS does not affect appetite suppression.
To investigate further, a randomized crossover study was conducted, enlisting a total of eight healthy adults, equally representing both men and women. The participants, aged between 20 and 35 years, had low to moderate levels of regular physical activity. The recruitment for this study took place at the University of Kiel, Germany, between September 2020 and July 2021.
In order to prevent the effects of estrogen exposure during the female cycle, it was recommended that all women use hormonal contraceptives. Additionally, individuals with chronic diseases, pregnancy, alternative eating habits, food allergies, smoking, and high habitual physical activity were excluded from this study. Furthermore, one participant was excluded due to inaccurate estimations related to non-isocaloric energy intake with the ketogenic formula diet (KETO).
When comparing an isocaloric diet with a normal carbohydrate (CHO) content to a one-day isocaloric ketogenic diet (KD) with only 5% CHO, it was observed that the KD resulted in higher total energy expenditure (TEE) and sleeping energy expenditure (SEE). Interestingly, a similar effect was found in a separate study using a whole room indirect calorimeter (WRIC), where participants shifted from a normal 50% CHO-based diet to an isocaloric KD. In both cases, SEE and TEE increased by approximately 100 kcal/day, while physical activity and the thermic effect of food (TEF) remained constant.
Based on theoretical assumptions, it was estimated that the difference in CHO content between the KETO and the isocaloric formula diet (ISO) would result in a TEE increase of approximately 225 kcal/day. However, this value was not achieved within the first 24 hours of the KD intervention. Instead, a modest increase of about 100 kcal/day was observed, which could be attributed to the activation of energy-demanding pathways such as hepatic gluconeogenesis (GNG) and the triglyceride fatty acid cycle.
Compared to total fasting (FAST), the KETO intervention led to an increase in cumulative energy expenditure (EE). This finding suggested that the upregulation of energy-demanding pathways occurred after 16 hours of following a ketogenic diet. There was no significant difference in total nitrogen excretion and cumulative carbohydrate oxidation between FAST and KETO. The higher EE observed with KETO could be attributed to an elevation in the futile cycling of glucose and/or fatty acids, rather than solely relying on GNG. Additionally, due to its lower protein content compared to the EXO and ISO diets, KETO resulted in a lower thermic effect of food (TEF).
In this study, the one-day ketogenic diet (KD) was found to be an effective strategy for weight maintenance. This was due to its ability to increase total energy expenditure (TEE) and reduce voluntary energy intake, particularly when compared to a habitual carbohydrate-rich diet consisting of highly processed foods. However, these effects were not observed when participants consumed a low-processed food diet with a lower energy density.
Importantly, fasting was observed to enhance gluconeogenesis (GNG), ketogenesis, and ureagenesis. As a result, resting energy expenditure (REE) was higher during early fasting compared to the control condition. Fasting also led to an increase in sympathetic nervous system (SNS) activity. Additionally, when participants supplemented their diet with ketone salts (KS), there was a decrease in carbohydrate oxidation compared to the control condition. These findings align with a previous study that showed oral KS supplementation did not affect subjective appetite. The lack of appetite suppression may be attributed to the fact that a one-day KD or fasting only leads to a moderate increase in ketone levels.
The strength of this study lies in its utilization of the intra-individual cross-over design and the implementation of a highly standardized setting, specifically a Whole Room Indirect Calorimeter (WRIC). However, it is important to note that the study is limited by its small sample size. The findings of this study indicate that following a 24-hour ketogenic diet resulted in increased energy expenditure and aided in maintaining a neutral energy balance. On the other hand, the addition of exogenous ketone bodies to an isocaloric diet did not show any significant improvements in energy regulation. Furthermore, subjective appetite ratings revealed no discernible differences between the various interventions.
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