Fasting Triggers Protein Breakdown Warning
A study found elevated Blood Urea Nitrogen (BUN) levels in people practicing 12-14 hour intermittent fasting, indicating increased protein breakdown to avoid hypoglycemia. Separate research revealed that fasting and ketogenic diets deplete bone marrow plasma cells via BHB, potentially impairing vaccine antibody responses and immunity.
- Blood Urea Nitrogen (BUN) is a waste product from the breakdown of protein, and elevated levels can indicate that the kidneys are not filtering waste effectively. However, high BUN can also be caused by dehydration or a high-protein diet, factors that can be associated with fasting. - Research on fasting and kidney health has produced mixed results. One study involving patients with stage 3 or higher chronic kidney disease found that Ramadan fasting was associated with worsening kidney function. Conversely, a 2025 study on mice suggested intermittent fasting might protect against the progression from acute kidney injury to chronic kidney disease. - Beta-hydroxybutyrate (BHB), the primary ketone body produced during fasting and ketogenic diets, serves as an alternative energy source for the brain, heart, and muscles when glucose is scarce. Normal BHB levels are low, but can rise to 1–2 millimoles (mM) after a fast and even higher during prolonged starvation. - The impact of BHB on immunity appears complex; while it may deplete certain immune cells, it has also been shown to have anti-inflammatory effects. Specifically, BHB can inhibit a protein complex called the NLRP3 inflammasome, which is involved in triggering inflammation. - A study using mouse models from the Icahn School of Medicine at Mount Sinai found that skipping meals triggered a stress response in the brain. This led to a migration of immune cells called monocytes to the bone marrow, and upon re-feeding, their return to the bloodstream was linked to heightened inflammation and a reduced ability to fight infection. - Fasting's effect on vaccine response has also been examined in animal studies. In one experiment, mice that practiced alternate-day fasting during the period of influenza vaccination had a significantly lower survival rate (38.9%) when exposed to the virus compared to the normally fed group (72.2%). - The ketogenic diet has been linked to potential changes in bone health. Studies in mice have shown that a ketogenic diet can lead to bone loss by increasing bone marrow fat, which in turn reduces the number of bone-forming cells called osteoblasts.
