Understanding hormones is extraordinarily complex. They are always in flux, changing with age, stress, diet, disease and medication, and they can cause a myriad of unpleasant symptoms, from migraines to numbing body aches to mood swings.

Hormones can also conspire against weight loss.

While science has done much to help us understand hormones, research continues to uncover insights that explain their influence on our weight.

During the past decade, ghrelin (pronounced GRELL-IN) has received lots of attention, since researchers have found a link between it and the regulation of hunger. Ghrelin is a hormone that’s responsible for stimulating the appetite. Protein suppresses ghrelin, so ensuring about 25% of your calories come from protein will keep this hunger-inducing hormone at bay. That means, if you’re following a 2,000 calorie diet, 500 of those calories should be from protein.

The counterpart to ghrelin is leptin, a hormone that’s believed to be responsible for satiety. Interestingly, refined sugar and high-fructose corn syrup have been found to lower leptin levels, negating its benefits.

Cortisol is probably among the best known of our hormones. Frequently called the “stress hormone,” cortisol is released when we’re under pressure. When the adrenal gland releases cortisol, the body craves carbohydrates which replenish and sustain our energy. Eating high-fat and high-sugar foods in combination with elevated cortisol levels precipitates weight gain and the accumulation of belly fat, one of the major risk factors for heart disease. What to do? Combat cortisol with exercise, yoga, meditation and other stress-reducing efforts.

Peptide YY, or PYY, is produced by our intestines and released after we eat. The more protein we eat, the more PYY is secreted, which explains the mechanism of the popular Atkins diet. While an empty stomach suppresses the release of PYY, a full stomach containing protein will act as a natural appetite suppressant. Eating small, frequent meals that include protein will temper a ravenous appetite, or the need to mindlessly munch.

Then, there’s progesterone. Familiar to many women, this hormone increases around ovulation in anticipation of a potential pregnancy. This, in turn, stimulates women to eat more calories which would support a growing fetus. While this natural, biological rhythm can’t be prevented, I tell my clients that they shouldn’t fight it. Just be vigilant, going to the gym regularly during the two weeks before a period; make conscious food choices, and keep sweets out of the house. Days one through 14 of the menstrual cycle is when a woman should start a diet; healthy eating is easier. Otherwise, be prepared for that progesterone surge, and be patient.