Nutrition
Intermittent fasting: what the evidence says and when to prescribe it
Intermittent fasting is neither magic nor poison. Here is what the literature says, which clients respond, and when to avoid it.
Intermittent fasting (IF) is popular, but the clinical evidence is more nuanced than social media suggests. The practical question in clinic is not whether it works, but whether it works better than equivalent calorie restriction with meals spread across the day.
What the evidence shows
When total calories are matched, controlled trials show similar weight-loss results between IF and traditional restriction. Where IF often shines is adherence: for some clients, simplifying to 2 or 3 meals reduces daily decisions and cuts down on snacking.
Who tends to do well on it
- Healthy adults with stable schedules and office routines.
- Clients who cannot stick to 4-5 meals but can to 2-3.
- People who tolerate short fasts well (>14 hours).
When to avoid it
- History of disordered eating.
- Pregnancy, breastfeeding, and growth.
- Diabetes on hypoglycemic medication (hypoglycemia risk).
- Athletes on double sessions or with very high calorie needs.
Frequently asked questions
Does it speed up metabolism?
Not in any clinically relevant way. Any metabolic difference tends to be small and disappears once calories and protein are matched.
Which window is better: 16:8 or 18:6?
Whichever the client sustains without effort. Adherence matters more than the purity of the protocol.
About the author
Equipo Almendra
Editorial · Almendra
The Almendra editorial team brings together nutritionists, engineers, and product managers writing about how to run a modern nutrition practice.
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