Supplements for increasing metabolic activity can act at three different levels depending on the product:

1. basal metabolism;
2. diet-induced thermogenesis (DIT);
3. physical activity.

Their intake is recommended during periods when the diet is such that it does not adequately support the mechanisms responsible for metabolic acceleration, i.e. when eating a low-calorie, low-carbohydrate diet. More specifically, supplements that stimulate increased metabolic activity are indicated during the first weeks of the anabolic, or metabolic restoration phase, and the last weeks of the catabolic phase. It is a good idea to constantly monitor how the body reacts to changes in the diet so as to adjust the intake of these products according to actual needs. It is recommended to start with the minimum dosage and then gradually increase the amount taken up to the maximum dosage suggested by research or tolerated by the body. If, despite a dosage at or close to the limit, no significant positive effects (in terms of both success in the diet and absence of adverse effects) are observed, it would be desirable to change supplements. Indeed, individuals do not all react in the same way to each substance: some may have significant results even with the minimum dosage, others may need a higher dosage, and still others may not respond at all. It is precisely in the latter case that a new substance should be tried. For the same reason, caution and gradualness in removing this support from the diet with the gradual increase in calories and carbohydrates in the phases of the dietary cycle devoted to it is desirable. Supplements belonging to the thermogenic class that will be discussed here are green tea, yohimbine, guarana, antioxidants, guggulsterone, coleus forskohlii, 7-keto, citrus aurantium and inorganic phosphates.