Achievement and maintenance of weight loss in obese individuals has proven difficult. Many hypotheses have suggested potential biological mechanisms to explain why weight loss attempts often fail, and the surrounding obesogenic environment also seems an obvious candidate. Among the biological factors proposed is gender, and weight loss trials have frequently shown that females are less successful than males at losing weight and at maintaining weight loss.

Women's weight is influenced by the menstrual cycle, in which changes in hormonal levels and interactions work to modulate fertility. These hormones control the menstrual cycle and coordinate the required changes in energy intake, expenditure, and storage, whilst preparing the body for pregnancy every month. As reproduction is a primary biological function, these hormones may be such strong mediators of eating behavior that they influence the outcome of a weight loss attempt. The menstrual cycle should therefore be taken into consideration as a factor in the physiology of energy balance in premenopausal women.

The cycle can be divided into three phases: menstruation or early follicular phase (days 1-5), late follicular phase that lasts until ovulation (~days 6-14, and the luteal phase (days 15-28).

Studies have shown that in the luteal phase of the menstrual cycle, women's energy intake and energy expenditure are increased and women experience more frequent cravings for foods, particularly those high in carbohydrate and fat, than during the follicular phase. A trend towards reduced carbohydrate utilization and increased fat oxidation in the luteal phase has also been reported, together with prolonged time to exhaustion when exercising at submaximal intensities. This suggests that the potential of the underlying physiology related to each phase of the menstrual cycle may be worth considering as an element in strategies to optimize weight loss.

In 2010 the investigators carried out a 90-day randomized, controlled pilot study in order to gain feedback on and assess acceptance of the meal and exercise plans being used and to observe if less control visits than planed in the main study were sufficient to achieve good compliance. Twenty eight were sreened and 24 were included. Subjects were randomized to either program A (given meal and exercise plans in relation to phases of their menstrual cycles) or Program B (a reduced calorie diet, calorie-matched to program A). The pilot study showed that Group A (The Menstralean group) tended to have a greater average weight loss at 60 days (-5.29 vs -3.57 kg, p = 0.06) and 90 days (-4.22 vs -2.75 kgs, p = 0.2) compared to the control groups. There was a dropout rate of 27%. This was primarily due to an inadequate number of control visits and contact with the subjects. Thus the Menstralean program seems to have the potential to enhance weight loss in overweight and obese women. However, the main study has to be carried out with more subjects in each group in a longer duration and with more support and contact with the subjects.

The aim of the present trial is to examine the impact of the menstrual cycle on weight loss attempts in healthy overweight (BMI > 27 kg/m2) premenopausal women (18-40 years) randomized to two different weight management programs for a period of 6 months.

Inclusion Criteria:

• Healthy females between the ages of 18-40 (inclusive)
• BMI > 27 kg/m².
• Regular menstrual cycle (28 ± 4 days - with a maximum of 4 days within-subject variation in menstrual cycle duration.
• Weight stable (within ± 3-kg) 2 months prior to study inclusion
• Must use barrier contraception (e.g. male/female condom) for the study's duration
• Must be willing to follow the prescribed diet/exercise plan for the study's duration

Exclusion Criteria:

• On hormonal contraceptives (IUD are allowed) or any other daily use of medications which can make the subject unsuitable for inclusion in the study.
• Any significant health problem (history of cancer, HIV/AIDS, Diabetes, cardiovascular disease, untreated hypothyroidism, etc.)
• Restrictions against participating in cardiovascular exercise and strength training
• Any condition, which in the opinion of the investigator makes the subject unsuitable for inclusion in the study.
• Women who are pregnant,lactating, or planning to become pregnant during the study period