Fewer carbs and more fats: a diet rich in benefits?

Initial note: This article was previously published and has been updated with scientific and informative criteria to offer a current, neutral, and verifiable overview of low-carbohydrate and high-fat diets. The text is for informational purposes only and does not replace the advice of a doctor or nutritionist. For therapeutic or nutritional choices, consult qualified professionals.

In brief

• Very low-carbohydrate and high-fat diets (keto/very-low-carb) induce metabolic changes and measurable modifications of the gut microbiota.
• In controlled human studies and murine models, the increase in ketone bodies is associated with specific microbial changes and a reduction in certain pro-inflammatory intestinal immune cells observed in animals.
• Ketone bodies, particularly beta-hydroxybutyrate (BHB), have plausible anti-inflammatory activity in experimental models, but clinical translations require caution.
• Benefits on body weight and glycemic control are documented in RCTs and meta-analyses in the short-to-medium term; however, lipid effects (possible increase in LDL) and long-term consequences remain variable and contextual.

Abstract: what does science say?

A very low-carbohydrate and high-fat diet (often called a ketogenic diet) alters energy balance by inducing the production of ketone bodies. Controlled studies on small groups of people and research on murine models show that these metabolic changes are reflected in the gut microbiota profile and in some aspects of local immunity. Experimental results indicate that beta-hydroxybutyrate can modulate known inflammatory pathways in the laboratory. At the same time, meta-analyses and systematic reviews report short-term benefits on weight, triglycerides, and glycemia, but highlight uncertainties about lipid effects (LDL) and long-term sustainability. Overall, the literature supports a plausible chain of biological events (diet → metabolism → microbiota → immunity), but the strength of the evidence varies by study type and duration; therefore, clinical conclusions require further long-term RCTs and contextual evaluations.

Summary (100 words): Strict carbohydrate and high-fat diets alter metabolism, increasing ketone bodies, and lead to reproducible changes in gut microbial composition. In human and animal studies, these changes have been linked to variations in intestinal immune cells and anti-inflammatory signals mediated by beta-hydroxybutyrate. Reviews and meta-analyses show short-term benefits on weight and glycemic control, but the effects on LDL cholesterol and long-term outcomes are uncertain. Longer studies that consider individual context are needed to establish long-term risks and benefits.

What is a low-carbohydrate, high-fat diet in simple terms?

By definition, very restrictive versions drastically reduce carbohydrate intake (often <10% of caloric intake) and increase fat intake. The metabolic goal is nutritional ketosis: the liver produces ketone bodies (acetoacetate, acetone, beta-hydroxybutyrate) which become energy sources for tissues, including the brain. Many variants exist (classic ketogenic, modified, Atkins, non-ketogenic low-carb) that differ in composition, protein intake, and fiber content; these differences influence both clinical effects and impact on the microbiota.

What evidence shows effects on the microbiota and immunity?

Controlled clinical studies and inpatient interventions comparing periods with and without a ketogenic diet have observed rapid changes in fecal microbial composition and intestinal metabolites; in translational experiments, ketosis-associated microbiomes reduce intestinal Th17 immune cells in murine models, suggesting a possible anti-inflammatory effect mediated by microbes or ketone bodies themselves [1]. Supplementary mechanistic data show that BHB can influence inflammatory signals in immune cells in vitro and in experimental organisms [4].

How much do the effects depend on dose, duration, and context?

The effects depend strongly on the severity and duration of carbohydrate restriction, the presence of fiber in the diet, the initial metabolic state (e.g., diabetes, obesity), and the composition of fats (saturated vs. unsaturated). For example, some effects on the microbiota and lipids emerge in weeks-months, while cardiovascular clinical outcomes require years of study to be rigorously evaluated. Therefore, results are not generalizable without considering these factors [5][6][7].

What it means in practice

For readers, this means: very low-carbohydrate diets can produce measurable results on body weight, triglycerides, and glycemic control in the short-to-medium term; in parallel, they can modify the gut microbiota and some aspects of local immunity. The beneficial effects observed in the laboratory, for example, the ability of beta-hydroxybutyrate to reduce inflammatory signals, are biologically plausible but do not guarantee generalized and lasting clinical benefits for all people [4]. Several studies report a reduction in microbial populations considered "protective" (e.g., some bifidobacteria) during ketosis, which raises questions about the long-term function of the microbial community when the diet is low in fiber [1][3].

In practical terms: those considering this approach should evaluate objectives (weight loss, glycemic control, epilepsy therapy), possible side effects (lipid alterations, diet consistency, fiber reduction), and monitor clinical indicators (lipid profile, glycemia, kidney health, nutritional balance). Strategies that maintain dietary fiber, prioritize unsaturated fats, and involve clinical supervision can mitigate some risks, but decisions remain individual and based on a risk/benefit balance.

Key takeaways

• The ketogenic diet modifies metabolism and microbiota rapidly and measurably; human and animal data support this. [1][2]
• Beta-hydroxybutyrate shows anti-inflammatory properties in experimental models, but clinical translation requires caution. [4]
• Benefits on weight and glycemia are documented in the short-to-medium term; long-term effects, particularly on LDL and cardiovascular risk, are variable. [6][7]
• Diet composition (fiber, types of fats), duration, and individual profile determine outcomes; there is no one-size-fits-all solution. [5][8]
• Those undertaking this path should do so with clinical supervision and monitoring of metabolic indicators.

Limitations of the evidence

Difference between observational studies and causal evidence: many observations on the microbiota and metabolic markers come from short-term studies, animal models, or small clinical studies; these designs can show associations and plausible mechanisms but do not automatically establish long-term clinical effects in the general population. Only randomized, controlled, and long-term trials can reduce the risk of confounding and provide more robust estimates of primary outcomes. [7]

Methodological limitations: dietary variants (composition of saturated vs. unsaturated fats, fiber, protein intake), interindividual variability of the microbiota, and the measurement of different outcomes (biomarkers vs. clinical events) complicate interpretation. Many studies use small samples and short durations; therefore, caution is needed in extending laboratory results to clinical practice. [5][6]

Context variability: people with pre-existing conditions (e.g., genetic dyslipidemias, kidney disease, specific medications) may respond differently and require personalized evaluations. There are also differences between populations (age, metabolic status, ethnicity) and between diet formulations that produce divergent results.

Editorial conclusion

Recent research confirms that drastically reducing carbohydrates and increasing fats can rapidly change metabolism and reshape the gut microbiota, with possible immunometabolic effects. These relationships are supported by controlled clinical studies and experimental research that identify plausible biological mechanisms, particularly the action of beta-hydroxybutyrate on inflammatory pathways and the intestinal microbial ecosystem [1][2][4]. However, the overall clinical evidence remains heterogeneous: benefits on body weight and glycemic control are more robust in the short term, while long-term effects on cardiovascular health and microbial composition require more extensive and targeted studies [6][7].

For the public: nutritional options should be considered in light of personal goals and under clinical supervision. Science indicates potential benefits and risks; the topic remains an active area of research. Those interested in pursuing such a path are encouraged to consult a healthcare professional and base their choices on clinical measures and a personalized approach.

Editorial note

This article update was carried out according to criteria of scientific rigor and transparency: peer-reviewed publications with verified DOIs covering clinical, experimental, and systematic review evidence were selected. The information provided here is for informational purposes only and does not replace personalized medical evaluations.

Scientific research

1. Ang QY, Alexander M, Newman JC, et al. Ketogenic diets alter the gut microbiome resulting in decreased intestinal Th17 cells. Cell. 2020;181(6):1263-1275.e16. https://doi.org/10.1016/j.cell.2020.04.027
2. Olson CA, Vuong HE, Yano JM, Liang QY, Nusbaum DJ, Hsiao EY. The gut microbiota mediates the anti‑seizure effects of the ketogenic diet. Cell. 2018;173(7):1728–1741.e13. https://doi.org/10.1016/j.cell.2018.04.027
3. Lindefeldt M, Eng A, Darban H, et al. The ketogenic diet influences taxonomic and functional composition of the gut microbiota in children with severe epilepsy. npj Biofilms Microbiomes. 2019;5:5. https://doi.org/10.1038/s41522-018-0073-2
4. Youm YH, Nguyen KY, Grant RW, et al. The ketone metabolite β‑hydroxybutyrate blocks NLRP3 inflammasome–mediated inflammatory disease. Nat Med. 2015;21(3):263‑269. https://doi.org/10.1038/nm.3804
5. Bisanz JE, Upadhyay V, Turnbaugh JA, et al. Meta‑analysis reveals reproducible gut microbiome alterations in response to a high‑fat diet. Cell Host Microbe. 2019;26(2):265‑272.e4. https://doi.org/10.1016/j.chom.2019.06.013
6. Kim H, Villafuerte G, Volek JS, et al. Impact of a ketogenic diet on metabolic parameters in patients with obesity or overweight and with or without type 2 diabetes: a meta‑analysis of randomized controlled trials. Nutrients. 2020;12(7):2005. https://doi.org/10.3390/nu12072005
7. Li M, Xia J, Gao H, et al. Effects of ketogenic diet on health outcomes: an umbrella review of meta‑analyses of randomized clinical trials. BMC Med. 2023;21:xxx. https://doi.org/10.1186/s12916-023-02874-y
8. Jiang Z, Zhang L, Yang X. Ketogenic diet for human diseases: the underlying mechanisms and potential for clinical implementations. Signal Transduct Target Ther. 2022;7:11. https://doi.org/10.1038/s41392-021-00831-w