In this wide-ranging conversation from 2010, Dr. Scott Connelly reframes metabolism through the lens of insulin and glucose homeostasis, arguing that insulin is the primary regulator of energy allocation, disease risk, and body composition. Drawing on cancer biology, epidemiology, and comparative physiology, he revisits the Warburg observation that malignant cells exhibit extreme “glucose avidity,” clarifying that while high glycolytic rates do not initiate cancer, they are driven by insulin-pathway signaling (notably AKT) and are a shared feature of transformed cells. Connelly emphasizes that glucose is both essential and toxic: the brain’s absolute dependence on glucose forces the body to tightly regulate blood sugar, using insulin to direct fuel toward oxidation or long-term storage—primarily fat.
Rejecting the simplistic “calories in, calories out” model, Connelly explains that humans are open, non-equilibrium systems in which insulin dynamically alters how efficiently energy is stored or dissipated. Dramatic changes in fat mass can occur without changes in caloric intake when insulin sensitivity shifts, as seen in diabetes, steroid use, fatty-acid ratios, and evolutionary adaptations. He distinguishes between metabolically healthy obesity and pathological insulin resistance, identifying dysregulated liver glucose production alongside insulin-sensitive fat storage as a key driver of cardiovascular disease. The practical takeaway is that in modern Western populations, controlling carbohydrate intake is the most powerful lever for health. His baseline prescription—heavy resistance training, high protein intake, restrained carbohydrates, and particular caution with fructose—targets insulin first, with improvements in body composition and disease risk following downstream.
This video, by BSI’s co-founder, was originally published in The CrossFit Journal. While Greg Glassman no longer owns CrossFit Inc., his writings and ideas revolutionized the world of fitness, and are reproduced here.
Coach Glassman named his training methodology ‘CrossFit,’ which became a trademarked term owned by CrossFit Inc. In order to preserve his writings in their original form, references to ‘CrossFit’ remain in this video.
Greg Glassman founded CrossFit, a fitness revolution. Under Glassman’s leadership there were around 4 million CrossFitters, 300,000 CrossFit coaches and 15,000 physical locations, known as affiliates, where his prescribed methodology: constantly varied functional movements executed at high intensity, were practiced daily. CrossFit became known as the solution to the world’s greatest problem, chronic illness.
In 2002, he became the first person in exercise physiology to apply a scientific definition to the word fitness. As the son of an aerospace engineer, Glassman learned the principles of science at a young age. Through observations, experimentation, testing, and retesting, Glassman created a program that brought unprecedented results to his clients. He shared his methodology with the world through The CrossFit Journal and in-person seminars. Harvard Business School proclaimed that CrossFit was the world’s fastest growing business.
The business, which challenged conventional business models and financially upset the health and wellness industry, brought plenty of negative attention to Glassman and CrossFit. The company’s low carbohydrate nutrition prescription threatened the sugar industry and led to a series of lawsuits after a peer-reviewed journal falsified data claiming Glassman’s methodology caused injuries. A federal judge called it the biggest case of scientific misconduct and fraud she’d seen in all her years on the bench. After this experience Glassman developed a deep interest in the corruption of modern science for private interests. He launched CrossFit Health which mobilized 20,000 doctors who knew from their experiences with CrossFit that Glassman’s methodology prevented and cured chronic diseases. Glassman networked the doctors, exposed them to researchers in a variety of fields and encouraged them to work together and further support efforts to expose the problems in medicine and work together on preventative measures.
In 2020, Greg sold CrossFit and focused his attention on the broader issues in modern science. He’d learned from his experience in fitness that areas of study without definitions, without ways of measuring and replicating results are ripe for corruption and manipulation.
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