The reason why meal replacement biscuits are considered to be helpful to lose weight is mainly because their design and formula make them low-calorie foods, thus helping to control the amount of energy intake. Here are some possible reasons:

1. Control calorie intake: Meal replacement biscuits are usually designed as low-calorie foods with relatively low energy density. This means that by eating meal replacement biscuits, you can get the nutrients you need while reducing your calorie intake.

2. High dietary fiber content: Meal replacement biscuits are usually rich in dietary fiber, which is a carbohydrate that the human body cannot digest and absorb. Dietary fiber helps to increase satiety and delay gastric emptying time, thus making you feel full for a longer time and reducing your desire to eat.

3. Control the intake of carbohydrates and sugar: Meal replacement biscuits usually control the content of carbohydrates and sugar to avoid causing rapid rise of blood sugar and excessive insulin release. This can help stabilize blood sugar levels and reduce hunger and appetite.

However, it should be noted that meal replacement cookies are not the only way to lose weight, and long-term dependence on meal replacement cookies may lead to nutritional imbalance. The most important thing in the process of losing weight is to adopt a comprehensive and healthy diet and moderate exercise, and establish good living habits. It is best to consult a professional doctor or dietitian before making any weight loss plan.