Ketogenic diets (KDs) are diets in which the net carbohydrate intake, calculated by subtracting fibres from total carbohydrates, is between 20 and 50 g/day (<10% of total energy intake) with a variable proportion of proteins and fats (Noakes, Windt 2017). In these conditions, glycogen stores are depleted (Paoli, Canato et al. 2011), insulin level is low and energy metabolism is mainly dependent from fat oxidation. KDs lead a significant increase in circulating levels of ketone bodies (KBs) β-hydroxybutyrate (βOHB), acetoacetate (AcAc) and acetone (Veldhorst, Westerterp et al. 2010). While AcAc and βOHB are used as energy, acetone is a volatile compound and is eliminated through expiration, giving the “sweet” breath odour typical of ketosis, or via renal excretion (Paoli, Canato et al. 2011). The concentration of KBs in the blood of healthy individuals during the carbohydrate fed state is about 0.1 mmol/L and increases to about 0.3 mmol/L after an overnight fast, but after prolonged fasting up to 20 days KBs can increase to more than 10 mmol/L. A diet is considered “ketogenic” when produces a stable increase in the level of βOHB higher than 0.6 mmol/L (Wiggam, O'Kane et al. 1997) or when the molar ratio of blood glucose to blood ketone body βOHB is less than or equal to 1 (Meidenbauer, Mukherjee et al. 2015). Since KBs AcAc and βOHB are acids, the ketosis state implies a condition of acidosis. Given the fact that the pH of the blood is 7.4 and that the pKa of AcAc is 3.8 and that of βOHB is 4.8, these acids circulate in the blood in a completely dissociated form and are eliminated together with sodium and potassium ions (Siliprandi & Tettamanti 2011). This loss of cations implies a decrease of pH, which is normally balanced from the body apart when potassium and sodium intake are impaired (Phinney 2004) or in pathological overproduction of KBs during untreated diabetes type 1 which leads to diabetic ketoacidosis, characterized by a KBs level higher than 20 mmol/L with a decrease of pH. Biochemistry Hans Krebs was the first who diversified physiologic from pathologic ketosis (Krebs 1966). For skeletal and cardiac muscle, which usually oxidize fats, the use of KBs is a relative advantage, while for the central nervous system, in which the entrance of fatty acids is prevented from the blood-brain-barrier (BBB), the availability of KBs is an important surrogate of glucose, which is the habitual substrate of nervous tissue. During starvation, under a ketogenic diet or in new-born infants, the brain can utilize KBs as primary fuel instead of glucose (Laeger, Metges et al. 2010) in proportion to the degree of ketosis (Hartman, Gasior et al.). βOHB is the most abundant circulating ketone body and its transport across the blood-brain barrier is mediated both by diffusion and by several monocarboxylic acid transporters as MCT1 and MCT2, the former being upregulated during a ketogenic diet (Newman, Verdin 2014). This complementary action between the liver, which produces KBs in periods of shortage of carbs, and the CNS which use them, it’s a very important event which was determinant for the survival of the human species over the millennia.
My research focused on three important aspects of KDs and weight loss, which needed further investigation:
1. long-term successful weight loss after a KD: the maintenance of weight loss over long time is challenging and the fear of weight regain is common, so that this phenomenon is named “yo-yo” effect. In this regard, low-carbohydrate diets are known to bring better results compared to low-fat diets in terms of weight loss (Shai, Schwarzfuchs et al. 2008) but not of compliance (Greenberg, Stampfer et al. 2009). Recently, Sumithran and colleagues have demonstrated that the increase in circulating ghrelin and in subjective appetite, which accompanied a hypocaloric diet, was reduced with a ketogenic approach (Sumithran, Prendergast et al. 2013). Thus, we hypothesized that certain aspects of the KD such as muscle mass retention, RMR (resting metabolic rate) and orexigenic hormone stability combined with the acknowledged health benefits of traditional Mediterranean nutrition may favour long-term weight loss. The aim of our study was to investigate the effect on weight and body composition of two short periods of a modified KD, i.e., a very low carbohydrate ketogenic diet with phytoextracts (KEMEPHY) (Paoli, Cenci et al. 2010, Paoli 2011, Paoli 2012) interspersed between longer periods of maintenance nutrition, based on the traditional Mediterranean diet, over a total period of 12 months in obese/overweight healthy subjects and was designed as a retrospective study. We analysed 89 male and female subjects, aged between 25 and 65 years who were overall healthy apart from being obese (mean BMI 35.82 ± 4.11 kg/m2). Data from this study demonstrate that the majority of subjects showed significant weight loss (10%) as a result of a two-phase KD and were compliant both during the six month weight loss phase and the six month normocaloric maintenance phase, with no weight regain. Moreover, the proposed protocol led improvements in health risk factors (total cholesterol, LDL cholesterol, triglycerides and glucose levels) in the majority of subjects. Compliance was very high which was a key determinant of the results seen;
2. formulation of new low-carbohydrate ultraprocessed foods to overcome the lack of sweet taste during a KD: a point of interest, which has always been a detrimental aspect of KDs, is the lack of sweet taste, which could be difficult to sustain for long periods, especially for people with a high sweet food preference. During consumption of a KD, it is mandatory to maintain a low level of glycaemia (about 80–90 mg/dL) to avoid insulin spikes (Paoli, Canato et al. 2011). This condition allows subjects to improve their fat oxidation as demonstrated by Paoli et al. (Paoli, Grimaldi et al. 2012) and by Tagliabue et al. (Tagliabue, Bertoli et al. 2012). Today the new food technology, which is able to build ultra-processed products very low in sugar content and high in protein and fibres, can help to solve this problem, formulating products with a high palatability and ready-to-consume format, useful both in ketosis and in easier low carb diets. Usually, ultra-processed products lack in proteins and fibres and produce postprandial glucose and insulin spikes (PAHO WHO 2015). This effect is known to elicit food craving and overeating, with a preference for high-glycaemic index carbohydrates (high-GI CHO) (Lennerz, Alsop et al. 2013), a phenomenon defined as CHO-craving effect (Ventura, Santander et al. 2014). In order to analyse the effect of 10 different high-protein low-CHO proprietary foods on glycaemia, we recruited 14 healthy females, which were tested for their glycaemic response through the glycaemic score (GS) method. All test foods, compared with glucose, produced a significantly lower glycaemic response and their GS resulted lower than 25 (compared to the reference GS value of glucose which is 100). We concluded that the reformulation of ultraprocessed ready-to-consume foods in a low-CHO, high-protein version can produce a significantly lower glycaemic response whilst maintaining the valued ready-to-use format and high palatability demanded by consumers, facilitating the adherence to a KD of individuals who tend to have a high preference for sweet foods;
3. effect of KDs on cognitive functions: the range of variation of glucose and ketone bodies (KBs) in the blood of non-diabetic individuals is wide and both of them can be used as energy from the brain. Data on glycaemia and ketonemia effects on cognitive functions on healthy humans following different diets are scarce. The purpose of this study was then to compare the effects of glycaemia and ketonemia variation after ten days of two different ketogenic diets and a calorie-restricted Mediterranean diet (MD) on working memory and executive functions in 63 sedentary healthy overweight (BMI>25) young women (age: 20-35), which were recruited in the university area. Subjects were divided in groups according to the day of the beginning of their follicular phase in order to minimize hormonal effects on mood and came for the basal measurements five days before the start of the dietary protocol. The following controls were set on the starting day of the diet (t1), on the third (t3), on the fifth (t5), on the seventh (t7) and on the last day (t10). On the basal control day, the weight of the subjects was measured and a body impedance analysis was performed. Subjects took a standard high carb breakfast and afterwards they completed the psychological tests. At t1, t3, t5, t7 and t10 ketone bodies levels and glycaemia were measured, as well as appetite levels. On the last control day (t10) subjects repeated the body impedance analysis, the body weight measure and, after breakfast (each group had a different breakfast according to the prescribed diet), the psychological tests. Psychological tests consisted in a mood test, two cognitive tasks, one to investigate working memory (visuo-spatial n back) and the second to stress executive functions (inhibitory control task) and in a VAS scale to test the appetite level. 45 subjects completed the study. Considering all participants together, pre-diet glucose levels were positively correlated with reaction time in the go-trial of the executive function test (r(43) = 0.358, p = 0.018), but this relation was not found in the post-diet measure both when subjects were analysed all together and when subjects were divided according to the type of diet followed. In the same psychological test, in the post-diet measure ketonemia showed a negative correlation with accuracy of the no-go trials (r(29) = -0.455, p = 0.027). We can conclude that healthy young overweight subjects with fasting glycaemia below prediabetes level were negatively affected by a high-carb breakfast during an executive function test. Moreover, the effect of mild KBs levels (2 ± 1.3 mmol/L) negatively affected accuracy of the no-go trials of the executive functions test
