Answer:

First off, 140 pounds for a height of 5’6” makes your BMI 22.6, within a healthy range (18.5-24.9). In general terms, 1,200 calories for women and ,1500 calories for men have long been used as minimum recommended intake levels. Even at these amounts it’s difficult to meet vitamin and mineral requirements unless one’s diet is exceptionally nutrient-rich and balanced. 

Using personalized estimates based on standardized equations is more predictive of actual needs. Using your age, height, weight and gender, your calculated base energy requirement, called basal metabolic rate (BMR), is 1,352-1,376 calories daily*. Your body composition, genetics and physiology, among other factors, determine your true metabolic rate which may be higher or lower than estimated. 

It’s not advised to reduce intake to BMR minimum very long for successful fat loss. Restricting intake to that level creates such an energy deficit that lean mass starts to break down for fuel. The scale may show a weight drop – often significant – from the water released as stored glycogen is used to fill the energy gap. Neither of these conditions foster fat burning or improve body composition.  

My best advice is to increase physical activity which will help retain lean mass and allow you to get sufficient nutrients from a more generous diet. There’s a lot of nutrition you can pack into 150 calories of wholesome foods. A yogurt parfait or bowl of crunchy popcorn is worth a half hour of dancing, recreational biking or swimming in my book! 

*based on Mifflin–St. Jeor and WHO equations. 

Suggested further reading: 

Resting Metabolic Rate: Best Ways to Measure It – And Raise It, Too https://www.acefitness.org/certifiednewsarticle/2882/resting-metabolic-rate-best-ways-to-measure-it-and/ 

Calories Burned in 30 Minutes For People of Three Different Weights https://www.health.harvard.edu/diet-and-weight-loss/calories-burned-in-30-minutes-of-leisure-and-routine-activities 

– Debbie J., MS, RD