Why You’re Gaining Fat in a Calorie Deficit: Hormones & Timing in Women

Sims emphasizes that many women skip eating before early workouts, thinking they can't stomach food, but this small intake is crucial to prevent the body from perceiving stress and breaking down muscle. The carbohydrate provides immediate fuel, and the protein (for strength sessions) supports muscle preservation. This pre-fueling, combined with a timely post-workout breakfast, sets up a positive metabolic signal for the day.

This recommendation follows the pre-exercise fuel. Sims stresses that the post-workout meal should be a substantial protein dose to capitalize on the anabolic window and to set the tone for regular eating throughout the day. She notes that this protein amount is larger than typical breakfasts, but necessary for women to maintain muscle mass and metabolic health.

Sims contrasts this with the popular noon-7pm fasting window, which she says leads to fat gain and endocrine dysfunction. The early window ensures that the body receives fuel when it is most active and insulin sensitive, and that digestion is complete before sleep, promoting restorative sleep and reducing fat storage signals. She ties this to research showing clear benefits for body composition and metabolic markers.

This is a general principle to avoid long gaps without nutrition that could trigger the hypothalamus to slow metabolism. Sims doesn't give exact numbers for lunch and dinner but implies that consistent protein and carb intake across meals supports energy and muscle maintenance.

Sims explains that if the body is still digesting food, it cannot fully shift into the parasympathetic mode required for quality sleep architecture. Poor sleep then feeds forward into metabolic dysfunction, poor glucose control, and increased fat storage. This rule is part of the early eating window strategy.

She explains that women who delay eating until noon and restrict calories can still gain body fat, while those who eat more in the morning and less in the evening lose fat, even if total calories are the same. This is due to the brain's hypothalamus sensing nutrient availability and adjusting metabolism, thyroid function, and muscle preservation. Ultra-processed foods and on-the-go eating further dysregulate appetite hormones. She emphasizes that exercise alone cannot burn enough calories to offset these metabolic shifts.

She details that delaying food intake until noon, even with an 8-hour eating window ending at 7pm, leads to more body fat gain, endocrine dysfunction, and metabolic issues. In contrast, starting at 7-8am and finishing by 4-5pm aligns with circadian rhythms—fueling when active and allowing the body to wind down without digestion before sleep. This early window also supports better sleep, which is crucial for weight loss, as late eating disrupts sleep architecture and blood glucose control, further signaling the brain to conserve fat.

Sims explains that the hypothalamus, sensitive to nutrition and tied to menstrual cycle and thyroid, perceives low energy availability as a threat. It breaks down metabolically hungry muscle tissue for fuel and simultaneously conserves fat. This leads to sarcopenia—muscle infiltrated with fat droplets, like marbled beef—reducing functional muscle quality. Thyroid function drops after just 4 days of low energy intake, slowing metabolism further. Women with pre-existing hypothyroidism are especially vulnerable and may need medication adjustments. The solution is to fuel adequately for activity, not delay eating.