The one-meal-a-day (OMAD) diet, an extreme form of intermittent fasting, has gained popularity for its simplicity and potential for rapid weight loss. The concept involves fasting for about 23 hours and consuming all daily calories within a single one-hour window. While many adherents report benefits like weight loss and improved focus, the impact on key health markers, particularly cholesterol, is a significant area of concern for researchers and healthcare providers.
The Scientific Evidence on OMAD and Cholesterol
Several studies have investigated the effect of reduced meal frequency on cardiovascular health indicators. The evidence is not uniform, but multiple findings point to a potential risk regarding cholesterol levels with a very restricted eating window, such as OMAD.
Increased LDL and Total Cholesterol
One of the most cited studies on this topic, published in the Journal of Clinical Nutrition, found that participants who switched from eating three meals a day to one meal a day experienced significant increases in total cholesterol and LDL ('bad') cholesterol. This effect was observed even in healthy, normal-weight individuals. The reasons for this increase are still under investigation, but it's believed to be related to metabolic stress and the body's response to prolonged fasting and subsequent refeeding.
Conflicting Findings and Study Limitations
While some studies show negative effects, other research on intermittent fasting, a broader category that includes OMAD, has shown positive or neutral impacts on cholesterol. Some studies have found that intermittent fasting may help lower LDL cholesterol and triglycerides while increasing HDL ('good') cholesterol. These inconsistencies likely arise from differences in study design, participant demographics, the duration of the fast, and, critically, the nutritional composition of the single meal. Many studies on IF, for instance, don't focus specifically on the 23:1 OMAD protocol, making it difficult to draw direct conclusions for this extreme fasting style.
The Impact of Meal Composition
Experts stress that the quality of the one meal is paramount. If the single meal is high in saturated fats, heavily processed foods, or simple carbohydrates, it can contribute to a spike in cholesterol levels and blood pressure. Conversely, a nutrient-dense meal rich in healthy fats, fiber, lean protein, and vitamins could have a more favorable effect. The risk lies in the potential for overeating unhealthy, calorie-dense foods during the eating window due to extreme hunger.
Comparison of Eating Patterns and Cholesterol
| Feature | OMAD (One Meal a Day) | Traditional (3+ Meals a Day) | Less Extreme Intermittent Fasting (e.g., 16:8) |
|---|---|---|---|
| Meal Frequency | Once per 24 hours | 3 or more times per day | Restricted eating window (e.g., 8 hours) |
| Cholesterol Impact | Potential for increased total and LDL cholesterol | Stable or managed levels with a balanced diet | Potential for improved LDL/HDL ratio and triglycerides |
| Metabolic Stress | Higher potential due to prolonged fasting | Lower, more stable insulin and blood sugar | Modest improvements in insulin sensitivity |
| Sustainability | Very difficult for most people long-term | Generally sustainable, socially integrated | Often more sustainable than OMAD |
| Nutrient Intake | High risk of nutrient deficiencies | Easier to meet daily nutritional needs | Adequate nutrient intake is feasible |
Other Health Risks of the OMAD Diet
Beyond cholesterol concerns, the OMAD diet presents several other potential health risks. Many users experience symptoms such as nausea, dizziness, irritability, and fatigue. The long fasting periods can also lead to nutrient deficiencies, particularly if the single meal lacks variety. Furthermore, there is a risk of muscle mass loss, especially with intense exercise, and the diet may not be suitable for pregnant or breastfeeding women, individuals with diabetes, or those with a history of eating disorders. Some studies even link extreme time-restricted eating to a higher risk of cardiovascular death.
Conclusion
While some proponents of the OMAD diet claim it can improve cholesterol, scientific evidence, including a notable controlled trial, suggests it may actually increase total and LDL cholesterol for some individuals. This effect appears to be particularly pronounced with extreme, prolonged fasting. The potential negative impact on cholesterol, combined with other risks like nutrient deficiencies and metabolic stress, indicates that OMAD is not a universally safe or recommended dietary strategy, especially for long-term use. For those concerned about heart health, more moderate and evidence-backed eating patterns are often a safer and more sustainable approach. It is always crucial to consult a healthcare provider before starting any extreme fasting regimen to ensure it aligns with your health needs and goals. For more detailed health information, consult the National Institutes of Health.
