- ✓Both regular AND irregular breakfast skipping impaired blood vessel function within 8 days — even occasional skipping carries risk
- ✓Fasting insulin rose significantly in breakfast skippers, signaling early insulin resistance relevant to diabetes management
- ✓Rigorous crossover trial design means the same participants experienced all conditions, strengthening the reliability of findings
| Country | Japan |
| Journal | Nutrients |
| Year | 2025 |
| Authors | Kashima, Morinaka, Endo |
| PMID | 41156497 |
A Study from Japan Links Breakfast Skipping to Damaged Blood Vessel Function
A study from Japan has uncovered a striking finding that could change how people with diabetes think about their morning meal: skipping breakfast — whether you do it every day or just some days — can measurably damage blood vessel health in as little as eight days. Researchers at the Prefectural University of Hiroshima used a carefully controlled clinical trial to show that both regular and irregular breakfast skippers experienced impaired vascular endothelial function (VEF) — a key early warning sign of cardiovascular disease.
What the Researchers Did
Ten healthy young adults participated in three separate nine-day trials in randomized order:
- Eat: Three regular meals per day, including breakfast
- Skip: Breakfast skipped every day for eight consecutive days
- Eat/Skip: Breakfast eaten one day, skipped the next, alternating throughout
Blood vessel function was measured using flow-mediated dilation (FMD) of the brachial artery — the artery in your upper arm. FMD measures how well blood vessels expand in response to increased blood flow, and is considered one of the most reliable non-invasive markers of early cardiovascular risk. Continuous glucose monitoring tracked blood sugar throughout, and blood samples measured insulin, free fatty acids, and triglycerides.
What They Found
By Day 9, both the regular skippers and the alternating skippers showed significantly worse blood vessel function compared to those who ate breakfast consistently. Perhaps most concerning: fasting insulin levels were significantly elevated in both skipping groups, suggesting early signs of insulin resistance — a core concern for anyone managing or at risk for type 2 diabetes.
Exploratory data also pointed to a weak negative association between worsening blood vessel function and rising fasting blood glucose and insulin levels over the eight-day period — meaning as glucose and insulin crept up, blood vessel performance declined.
Why the Japanese Perspective Is Valuable
Japan has one of the world's most studied populations for cardiometabolic disease, with decades of nutritional epidemiology data. Japanese dietary research often focuses on meal timing and structure with exceptional precision — offering insights that complement US-based studies. Importantly, this study used a crossover design, meaning the same participants experienced all three conditions, making it one of the most rigorous short-term breakfast studies conducted to date.
Converting the Numbers for US Patients
Blood glucose levels in this study were measured in mmol/L (standard outside the US). For reference:
- A normal fasting glucose of 5.6 mmol/L = 101 mg/dL (borderline per ADA guidelines)
- A fasting glucose of 7.0 mmol/L = 126 mg/dL (diabetes threshold per ADA)
The ADA currently recommends that people with diabetes aim for fasting glucose between 80–130 mg/dL. The elevated fasting insulin seen in skippers suggests the body is working harder to manage blood sugar — a red flag for insulin resistance.
⚕️ Why This Matters for US Patients
Intermittent fasting and breakfast skipping have become popular trends in the US, including among people with type 2 diabetes. But this research suggests that even occasionally skipping breakfast may begin to impair blood vessel health — and people with diabetes are already at two to four times the cardiovascular risk of the general population. Damaged endothelial function is a known precursor to atherosclerosis, heart attack, and stroke. If you are considering any fasting protocol, speak with your care team first. This study reinforces that consistent meal timing may be just as important as meal content for protecting your heart.
Study Limitations to Know
This was a small study (10 participants), conducted in healthy young adults without diabetes — so findings may not directly translate to older adults or those already managing blood sugar conditions. Larger studies in diverse populations are needed. That said, the crossover design and objective measurements add significant credibility to the findings.
Original study: Kashima, Morinaka, Endo. "Regular or Irregular Breakfast Skipping Suppresses the Vascular Endothelial Function of the Brachial Artery." Nutrients, 2025. PMID: 41156497. DOI: 10.3390/nu17203244. Clinical Trial: UMIN000053117.