Telogen effluvium from crash dieting typically begins 2 to 4 months after the restriction period and peaks at month 3 to 5. By tracking density alongside your dietary changes, you create a clear correlation record that documents both the damage from the diet and the recovery timeline once nutrition normalizes.
Why Crash Diets Cause Hair Loss
Hair follicles are among the most metabolically active cells in the body. They require a constant supply of calories, protein, iron, zinc, and B vitamins to maintain the growth cycle. When caloric intake drops sharply, the body deprioritizes non-essential functions, and hair growth is one of the first systems affected.
The mechanism is telogen effluvium: a large number of follicles are pushed from the growth phase (anagen) into the resting phase (telogen) simultaneously. After 2 to 3 months in the resting phase, those follicles release the hair shaft, causing diffuse shedding.
| Deficit Type | Risk of Hair Loss | Typical Onset |
|---|---|---|
| Moderate deficit (500 to 750 cal/day below TDEE) | Low | Unlikely unless prolonged beyond 3 months |
| Aggressive deficit (1,000+ cal/day below TDEE) | Moderate | 2 to 4 months |
| Very low calorie diet (under 800 cal/day) | High | 2 to 3 months |
| Complete fasting (water fasting, juice fasting) | Very high | 6 to 10 weeks |
| Protein-deficient restriction | Very high | 2 to 3 months regardless of calories |
The severity of shedding correlates with both the depth of the deficit and its duration. A 2-week juice cleanse may cause mild shedding. A 3-month crash diet under 1,000 calories per day can cause shedding severe enough to reduce visible density by 20 to 40%.
Step-by-Step: Track Diet-Related Hair Loss
Step 1. Establish a pre-diet baseline. If you are planning a period of caloric restriction, take a full density reading before you start. This baseline captures your starting density before any nutritional stress. Even if you have already started dieting, take a reading now to establish the earliest reference point available.
Step 2. Log your dietary details. In your myhairline.ai treatment log, record:
- Start date of caloric restriction
- Daily caloric intake (average)
- Daily protein intake (grams)
- Specific diet type (keto, intermittent fasting, liquid diet, etc.)
- Any supplements taken (iron, biotin, zinc, multivitamin)
- Duration of the restriction period
Step 3. Track density at 4-week intervals. Starting from the beginning of the diet, take density readings every 4 weeks. During the first 8 weeks, you may not see any changes because the delayed-shedding mechanism has not yet kicked in. Continue tracking through this quiet period because the data gap would make it harder to correlate the diet with later shedding.
Step 4. Document the shedding phase. When shedding begins (typically month 2 to 4), increase tracking frequency to every 2 weeks. This captures the rate of density decline during the peak shedding window. Also photograph your brush, pillow, and shower drain to document shedding volume visually.
Step 5. Log the return to normal nutrition. Record the date you resume adequate caloric intake. This becomes the anchor point for tracking your recovery timeline.
Step 6. Continue tracking through recovery. After resuming normal nutrition, maintain 4-week tracking intervals for at least 12 months. Recovery is gradual, and monthly readings document the upward trend that confirms your follicles are cycling back into active growth.
Reading Your Diet-Shedding Correlation Data
After completing a full tracking cycle (pre-diet through recovery), your data tells a specific story. Here is how to interpret common patterns.
2 to 3 month delay between diet start and shedding onset: This is the classic telogen effluvium pattern and strongly suggests the diet was the trigger. The more precise your diet start date and shedding onset date are in the data, the clearer this correlation becomes.
Shedding that begins during the diet: If density starts declining within the first 4 to 6 weeks of dieting, the cause may not be the caloric restriction alone. Other factors like stress, medication changes, or seasonal shedding could be contributing. Check whether other variables changed during the same period.
Shedding that continues more than 4 months after resuming normal nutrition: This may indicate a secondary condition. Crash diets can accelerate androgenetic alopecia in genetically predisposed individuals. If your tracking data shows continued decline despite adequate nutrition, consult a dermatologist. Your data provides the timeline they need to evaluate whether the pattern is consistent with telogen effluvium or pattern hair loss.
Nutritional Thresholds for Hair Health
Research identifies specific nutritional minimums for maintaining the hair growth cycle. If you are planning a deficit, staying above these thresholds reduces your risk of triggering shedding.
| Nutrient | Minimum Daily Intake for Hair Health | Common Deficit Sources |
|---|---|---|
| Protein | 0.8g per kg body weight | Vegan diets, juice cleanses, low-calorie plans |
| Iron | 18mg (women), 8mg (men) | Vegetarian diets, caloric restriction |
| Zinc | 8 to 11mg | Low-meat diets, severe restriction |
| Biotin | 30mcg | Rare to be deficient, but worth monitoring |
| Vitamin D | 600 to 1,000 IU | Indoor lifestyles, low-fat diets |
| Calories (total) | Over 1,200 for women, over 1,500 for men | Any aggressive deficit plan |
Tracking your nutrient intake alongside density readings creates a dual dataset that shows exactly which deficiencies correlate with which density changes.
Recovery Timeline After a Crash Diet
Once you return to adequate nutrition, the recovery follows a predictable curve that density tracking captures clearly.
Month 1 to 2 (post-diet): Shedding continues even after nutrition normalizes. This is expected because follicles that were already in the resting phase will complete their shedding cycle regardless of dietary changes.
Month 2 to 4: Shedding slows and stops. Density readings stabilize at their lowest point. New growth begins but is too short and thin to register on density scans.
Month 4 to 8: New growth becomes measurable. Density readings begin trending upward. This is the phase where tracking provides the most psychological benefit because you can see objective evidence of recovery.
Month 8 to 12: Continued recovery toward baseline. Most people recover 85 to 100% of their pre-diet density within this window, assuming the deficit did not unmask underlying androgenetic alopecia.
For a broader view of weight-loss-related hair changes, see our guide on hair loss tracking after weight loss. If your shedding pattern matches telogen effluvium, our telogen effluvium recovery guide covers treatment options during the recovery phase.
Start tracking the impact of dietary changes on your hair density at myhairline.ai/analyze.
This article is for informational purposes only and does not constitute medical or nutritional advice. Consult a healthcare professional before starting any restrictive diet and if you experience significant hair shedding.