If you eat a well balanced diet, cut out any added sugars, treats or savoury snacks, avoid alcohol and give 100% on all 20 sessions I would expect some of the following results for someone who is classed within the bracket of overweight or above BMI and high + body fat percentage.
Body fat reduction of 3 %. Increase skeletal muscle by 3 %. Minimum of 3 inch reduction from around waist and hip size. Loss of minimum one stone in bodyweight. Resting heart rate reduction of 10 beats per minute. Lowering of blood pressure and visceral fat levels. Increase in strength and cardiovascular fitness levels of 33%.
These are just a few of the small improvements that can be made if you can commit to just 4 weeks of your life.