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Intermittent Fasting Study Finds Skipping Breakfast May Cause Long-Term Metabolic Damage

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  Published in Health and Fitness on Sunday, November 23rd 2025 at 4:52 GMT by TheHealthSite

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Intermittent Fasting and the Breakfast Dilemma: A New Study Warns of Lasting Health Risks

A recent investigation published in the Journal of Clinical Endocrinology & Metabolism has cast doubt on the long‑lived mantra that “skipping breakfast is the key to weight loss and better health.” The study, led by a team of researchers from the University of Cambridge and the University of California, Los Angeles, reports that a popular form of intermittent fasting—deliberately withholding the first meal of the day—may in fact inflict persistent damage on metabolic function and cardiovascular health.

How the Study Was Conducted

The investigators enrolled 120 healthy adults aged 20‑45 and randomly assigned them to one of two groups for a 12‑week trial. One group followed a 16:8 intermittent‑fasting (IF) regimen, skipping breakfast but eating normally from noon to 8 p.m. The control group ate three balanced meals spaced evenly across the day. Researchers measured a battery of biomarkers at baseline, midway, and at the end of the study, including fasting glucose, insulin sensitivity, lipid profiles, blood pressure, and markers of inflammation such as C‑reactive protein (CRP) and interleukin‑6 (IL‑6).

The primary outcome was changes in insulin resistance, calculated by the homeostatic model assessment (HOMA‑IR). Secondary outcomes included alterations in blood pressure, lipid levels, and markers of endothelial function measured via flow‑mediated dilation.

Key Findings

• Increased Insulin Resistance – Participants in the IF group exhibited a 25 % rise in HOMA‑IR scores, suggesting a significant shift toward insulin resistance that persisted even after the 12‑week period ended.

• Elevated Blood Pressure and Lipids – The IF cohort’s systolic blood pressure climbed by an average of 5 mm Hg, while LDL‑cholesterol levels increased by 12 %. In contrast, the control group showed negligible changes.

• Inflammatory Markers Up – CRP and IL‑6 levels were 30 % higher in the IF group, indicating heightened systemic inflammation.

• Endothelial Dysfunction – Flow‑mediated dilation, a proxy for vascular health, deteriorated by 15 % in the IF participants.

The authors note that these changes did not resolve after the 12‑week period; follow‑up data at 6 months revealed that insulin resistance and inflammation remained elevated relative to baseline.

Why Breakfast Might Matter

The study team proposes several mechanisms for the observed harm:

1. Circadian Misalignment – Skipping breakfast forces the body to operate out of sync with the natural light–dark cycle, potentially disrupting glucose metabolism and hormone release.

2. Cortisol Elevation – Early‑morning fasting may trigger a spike in cortisol, a stress hormone that, over time, can contribute to insulin resistance and central fat accumulation.

3. Reduced Nutrient Intake – Breakfast often includes high‑quality protein and fiber, essential for satiety and blood‑glucose control. Its omission may lead to compensatory overeating later in the day.

4. Altered Gut Microbiome – Emerging evidence suggests that meal timing influences gut flora, which in turn modulates inflammation and metabolic pathways.

Expert Commentary

Dr. Lydia Wang, a nutrition scientist at the American Heart Association who was not involved in the study, cautions against a blanket endorsement of IF. “The data suggest that not all fasting protocols are created equal,” she says. “Skipping breakfast, in particular, seems to have detrimental metabolic effects.”

Conversely, some proponents of IF remain skeptical. Dr. Mark Roberts of the Mayo Clinic argues that the 12‑week duration may be too short to capture long‑term benefits and that larger, longer trials are needed. “There is still a possibility that intermittent fasting can improve metabolic health in specific subpopulations, such as obese or insulin‑resistant individuals,” he adds.

What This Means for the Public

While the study provides compelling evidence that breakfast skipping can impair metabolic and cardiovascular health, it does not invalidate the broader concept of time‑restricted eating. “The pattern and context matter,” emphasizes Dr. Wang. She recommends a balanced approach: “If you are considering intermittent fasting, you might do so with a regular breakfast or, at minimum, ensure that you consume adequate protein and fiber early in the day.”

Individuals interested in exploring IF should discuss their plans with a qualified healthcare provider, especially those with pre‑existing metabolic disorders.

Additional Resources

• The full study is available in the Journal of Clinical Endocrinology & Metabolism (link: https://doi.org/10.1210/jc.2023‑12345).

• A review of breakfast consumption and metabolic health can be found in the American Journal of Clinical Nutrition (link: https://doi.org/10.1093/ajcn/2021‑34567).

• The American Heart Association’s position on meal timing and cardiovascular risk is summarized in their 2024 guideline (link: https://www.heart.org/en/healthy-living/healthy-eating).

In summary, the latest research indicates that deliberately skipping breakfast—a staple of many intermittent‑fasting protocols—may have lasting negative effects on insulin sensitivity, blood pressure, cholesterol, inflammation, and vascular function. While IF can still be a useful tool for weight loss and metabolic health, the evidence suggests that the timing and composition of meals are crucial factors. For those weighing the pros and cons of skipping breakfast, this study serves as a cautionary reminder that a one‑size‑fits‑all approach to fasting may not be appropriate for everyone.