1 Leptin is a powerful and influential hormone produced by your fat cells. 2  It plays a key role in regulating energy intake and energy expenditure.
(Upgrades are not available on fares in the L, T, and U range, however, which are the most deeply discounted.) To calculate the price of an upgrade, Delta charges a dollar amount per 500 miles. $50: Up to 500 miles. $75: 501-1000 miles. $100: 1001-1500 miles.
1 To book a First Class upgrade using your Delta miles, call 1-800-800-1504.  Upgrade Offer: Mileage Upgrade Award is valid for upgraded one-way travel on Delta Air Lines-operated flights worldwide, including connecting flights, between the origin and destination of a ticketed fare.