The Ketogenic Diet, Immunometabolism and Optimal Immune System Function

Keto4Life

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May 24, 2021
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In the not-so-distant past it was believed that metabolism and immune systems in the body worked independently of each other. However, an ever-growing body of research has found that not only are they linked, but metabolic health plays an integral part in the healthy functioning of our immune systems. These discoveries have lead to a field of study of the integral functioning of these two systems referred to as immunometabolism.

Immunometabolism describes the changes that occur in intracellular metabolic pathways in immune cells during activation. Six major metabolic pathways have been studied in immune cells in detail: glycolysis, the tricarboxylic acid (TCA) cycle, the pentose phosphate pathway, fatty acid oxidation, fatty acid synthesis and amino acid metabolism. (*)

Researchers in Germany published a study in June of 2021 entitled Very-low-carbohydrate diet enhances human T-cell immunity through immunometabolic reprogramming. The authors of the study noted that there have been “unproven assumptions that ketone bodies positively affect human immunity” and set out to investigate this topic. Their claimed first of a kind study included “an in vitro model using primary human T cells and in an immuno-nutritional intervention study enrolling healthy volunteers. In vitro refers to a process “performed or taking place in a test tube, culture dish, or elsewhere outside a living organism: in vitro fertilization. The opposite of in vivo.”

The authors first provide evidence of how the Standard American Diet (SAD) has been progressively found to be at the origin of many of the common disease states found in society, such as, metabolic syndrome, autoimmune disorders, and cancer, leading to a decreased life expectancy in the 21st century. They follow this up with citations highlighting how the modern diet has been found to impair “cellular immunity and evokes systemic low-grade inflammation not only by causing obesity but also by direct reprogramming of immune cells toward a proinflammatory phenotype”. Before revealing the results of their study, the researchers point out that nutritional interventions may hold the key to what ails us, however current recommended dietary guidelines do not have substantial scientific support.

The ketogenic diet with its subsequent production of beta-hydroxybutyrate in the body has been shown to be anti-inflammatory (suppressing the NRLP3 inflammasome) in previous animal model studies, yet the authors indicate that “human adaptive immunity” had not been examined until now. The authors declare this study to be “the first study investigating the influence of KD on human immune responses in vitro and in a cohort of healthy subjects. Our results reveal profound beneficial effects of ketone bodies on human T-cell immunity.”

The Results
The researchers first reveal the results of their in vitro examinations. They cultivated “human peripheral blood mononuclear cells (PBMCs)” for 48h with a racemic mixture of beta-hydroxybutyrate (D/L-BHB). The BHB equated to approximately 5mM of D-BHB which nearly approaches the maximum endogenous ketone production in the body.

BHB improves human T-cell immune capacity

“BHB improves effector and regulatory T-cell function and primes human T memory cell differentiation both in vitro and in vivo. These functional changes are based on a fundamental immunometabolic reprogramming, resulting in enhanced mitochondrial oxidative metabolism, thus conferring an increased immunometabolic capacity to human T cells. We provide molecular evidence that ketone bodies promptly improve human T-cell metabolism and immunity. By complementing classical approaches of modern medicine, nutritional interventions offer new perspectives for prevention and therapy of numerous diseases.” This in vitro experiment revealed the following impact of BHB on human T-cell immunity:
  • BHB led to a significant transcriptional upregulation of CD4+ T-cell cytokines interleukin (IL)2, IL4, IL8, and IL22 (Fig 1A).
  • Protein analyses also showed an upregulation of IL2, IL4, IL6, and IL8 (Fig 1B). CD4+ subset analysis revealed a downregulation of the Th1 transcription factor Tbet—resulting in a decrease in Tbet/GATA3 ratio—yet no significant changes of the Th1/Th2 cell ratio (Fig 1C, Appendix Fig S1E).
  • CD8+ T-cell response displayed markedly increased levels of interferon γ (IFNγ), cytolytic proteins perforin 1 (PRF1) and granzyme B (GZMB), cytotoxic T lymphocyte-associated antigen 4 (CTLA4), and tumor necrosis factor alpha (TNFα; Fig 1D).
  • IFNγ and TNFα protein secretion was also elevated in response to BHB, and functional analysis unveiled enhanced cell lysis activity (Fig 1E).
  • Of note, in the absence of activating stimuli, unstimulated T cells did not exhibit relevant expression levels of immune cytokines, irrespective of their nutritional situation (Appendix Fig S1C and D).
“In summary, these findings clearly provide evidence for both improved effector and improved regulatory T-cell function, representing an enhanced global immune capacity of BHB+ primary human T cells.”

BHB increases mitochondrial aerobic oxidative metabolism in primary human T cells

Next, the researchers examined whether increases of energy supply would elicit the effects observed and set out to investigate “the functional impact of BHB on T-cell metabolism”. The observed effects were:
  • Increased maximal respiration and spare respiratory capacity (Fig 2A).
  • BHB+ CD4+ T cells exhibited elevated basal oxidative respiration (Fig 2B).
  • In CD8+ T cells, a marked shift toward oxidative metabolism—consisting of:
    • elevated basal and maximal respiratory rates,
    • mitochondrial ATP production,
    • and spare respiratory capacity—was displayed (Figs 2C and EV1A).
    • Notably, these alterations were not based on suppressed glycolysis, as BHB+ T cells retained their glycolytic capacity (Fig EV1B and C).
“Taken together, these data provide evidence for a substantial metabolic shift of T cells toward mitochondrial oxidative phosphorylation (OXPHOS) in response to BHB.”

BHB amplifies ROS production and directs T cells toward memory cell formation

The metabolic shift of T cells to enhanced mitochondrial oxidative phosphorylation in response to BHB exposure was also found to be supported by an amplification in ROS (reactive oxygen species). A caveat to this effect is that increased mitochondrial ROS production has been linked to mitochondrial and cellular damage (*). However, upon further investigation, the researchers found that there was also an increase cell protective antioxidant capacity within the immune cells providing a mitigating response to any potential damage. Going a step further, the authors also observed that mitochondrial cell integrity remained intact. “BHB did not alter mitochondrial membrane potential of primary human T cells, neither in CD4+ nor in CD8+T-cell subsets. Hence, ketone metabolism does not compromise mitochondrial integrity.”

In summary, an enhanced aerobic mitochondrial metabolism in response to BHB directs human T cells toward Tmem differentiation.” The significance of this effect is that once a new pathogen is eliminated within the body, new long lived memory T cells are produced that provide a more robust and quick response to eradicating the pathogen in the future if encountered once again.

Ketogenic diet in vivo

The second arm of this study included examining the effect of the ketogenic diet on immune response in humans. Forty-four healthy volunteers were placed on a ketogenic diet for three weeks. Carbohydrate consumption was limited to < 30g/day. Confirmation that the participants had entered into ketosis was verified by measuring ketones (BHB) in the blood and BHB levels were found to range between 1.0 – 1.5 mmol. The study participants tolerated the diet well with no significant adverse events. However, individuals who were overweight when starting the project found that they did encounter significant fat loss while on the diet while those with a normal BMI experienced “only marginal BMI changes”.

Transcriptome and gene set enrichment analysis reveals immunometabolic reprogramming of human T cells under the influence of KD
When examining the effect on the relevant genes involved in immunometabolism in the subjects while in ketosis, the researchers found significant changes in gene expression. Of particular note was the upregulation of a set genes referred to as Nur77. “Nur77 is known to indicate T-cell receptor signaling strength and is associated with memory cell development (Li et al, 2020; Shin et al, 2020). Notably, Nur77 has recently been identified as a central regulator of T-cell immunometabolism (Liebmann et al, 2018).”

The authors summarize: “these results highlight substantial transcriptomic changes in favor of T-cell action, memory cell differentiation, and oxidative metabolism, thus pointing to immunometabolic reprogramming of human CD4+ and CD8+ T cells through KD.”

KD enhances human T-cell immune capacity
The researchers were able to confirm in the human subjects the same enhanced T-cell function found in their in vitro studies. “Thus, these data demonstrate an enhanced human T-cell immune capacity through KD in vivo.”

KD strengthens mitochondrial metabolism and memory cell development
Similarly, further examination in humans provided additional confirmation of the data found in vitro showing upregulated mitochondrial metabolism, memory T cell formation and ROS production. Just as in the in vitro model, mitochondrial membrane structure and function were found not to be impaired or damaged. “In summary, KD led to an increase in mitochondrial mass, ROS production, and aerobic oxidative metabolism through enhanced respiratory chain activity. These KD-induced changes in human T-cell immunometabolism promote Tmem development.”

KD improves overall immune responses in vivo
In conclusion, the authors note the extremely complex nature of the human immune system and the role metabolism plays in its optimal functioning. The researcher’s approach “allowed for the detection of overall immune responses of adaptive and innate immune cells in a physiological environment during pathogen encounter.” In this examination they found the ketogenic diet “significantly reshaped human T-cell immunity toward a more powerful yet controlled adaptive immune response.” Dietary interventions are often ignored in the fight against disease. This study provides an excellent argument, especially in these days of Covid-19, for taking a closer look at the ketogenic diet in that good fight.
 
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