#605: Fasting, Nutrient Timing & CGMs: Interpreting the Evidence – Prof. James Betts

In this episode of Sigma Nutrition Radio, host Danny Lennon welcomes back Professor James Betts from the University of Bath to discuss the evolving evidence around fasting, nutrient timing, chrononutrition, and the use of continuous glucose monitors (CGMs). Betts, a leading expert in metabolic physiology, reflects on how the scientific understanding of time-restricted eating and intermittent fasting has shifted over the past five years. He emphasizes that early claims of significant metabolic benefits—such as increased energy expenditure or dramatic weight loss—have largely been overstated, with most effects now attributed to calorie restriction rather than timing itself. Instead, he highlights emerging interest in more nuanced physiological outcomes, such as insulin sensitivity, autophagy, inflammation, and microbiome interactions, particularly in controlled laboratory settings. Betts also critiques common methodological flaws in nutrition research, including non-randomized designs, within-group comparisons to baseline, and misleading use of responder analyses and waterfall plots. He stresses the importance of rigorous study design and critical interpretation of data, especially when translating findings to public health advice. The conversation then turns to chrononutrition—the strategic alignment of meals with circadian rhythms. Betts explains that while broad fasting windows may not offer unique benefits beyond calorie control, subtle shifts in macronutrient distribution (e.g., more carbs in the morning, more protein in the afternoon) could improve metabolic health by syncing with natural biological rhythms. He shares insights from his team’s complex studies using continuous feeding and muscle biopsies to track daily metabolic fluctuations. Finally, Betts offers a balanced view of CGMs, acknowledging their value in capturing real-time glucose patterns but warning against misinterpretation—especially the overemphasis on spikes and the mistaken belief that a single meal response defines long-term tolerance. He advocates for viewing CGM data as part of a broader pattern, not isolated peaks, and calls for repeat testing to validate individual responses. The episode concludes with Betts’ simple yet powerful advice: move your body daily, regardless of the complexity of nutrition science.