Korean pine nut oil (Pinnothin^®) is obtained by natural pressing of Korean pine nuts (P. koraiensis) and it contains triglycerides (TG) and more than 92% poly- and mono-unsaturated fatty acids (PUFAs and MUFAs) like pinolenic acid (C18:3), linoleic acid (C18:2) and oleic acid (C18:1) [1]. Korean pine nut oil is claimed to be unique in that it contains approximately 15% pinolenic acid (C18:3). Korean pine nut free fatty acids (FFA) significantly increase the release of satiety hormones such as cholecystokinin (CCK) [2]. CCK delays gastric emptying and produces a subsequent increased feeling of satiety and a decreased appetite. In terms of inducing satiety-hormone secretion, long chain fatty acids are more effective than medium chain fatty acids, PUFAs are more effective than MUFAs [3,4].

Pine nut FFA administration to overweight postmenopausal women has reported to produce a significant increase of CCK-8 and glucagon like peptide-1 (GLP-1). The appetite sensation "prospective food intake" and “desire to eat” are also lowered, and these effects last up to 4 hours [2,5]. Administration of Korean pine nut FFA (2 grams) reduced lunch ad-libitum food intake by 9% compared with the placebo control. This was achieved without increasing caloric intake during the evening meal which suggests there is no compensation for the lesser food intake during lunch [6]. So far no adverse effect of the compound during the study period or at post study debriefing have been reported.

Olibra^® is a fat emulsion formulated from palm oil (40%) and oat oil fractions (2.5%). Its mechanism of action is similar to that of Korean pine nut oil, increasing and prolonging the release of peptide YY, CCK and GLP-1 [7,8] which inhibit upper gut motility (to slow gastric emptying and intestinal transit) generating an indirect satiety effect [9,10].

Compared to other appetite suppressant products, the evidence supporting the effects of Olibra^® is more comprehensive. Double-blind, placebo-controlled reports indicate that Olibra^® administration to lean, overweight and obese individuals significantly reduced hunger and desire to eat [11] with a consequent decrease of energy and macronutrient intake up to 36 h post-consumption [7,12]. The results obtained with chronic administration suggest that Olibra^® could help to maintain weight after weight loss programmes [8]. Taken together these findings indicate that in addition to having acute effects on energy intake (EI) and hunger/satiety, Olibra^® could be beneficial for weight maintenance.

G. cambogia is a tree indigenous to southeast Asia. Commercially available (−)- hydroxycitric acid (HCA) extract from G. cambogia [Super CitriMax^® HCA-SXS (HCA-SX^®)] is mainly extracted from the dried and cured pericarp of the fruit of this species [13]. These pericarp rinds have been used for centuries in regional cooking practices and are reported to make meals more filling and satisfying [14,15], without any reported harmful effects. HCA may promote weight reduction through suppressed de novo fatty acid synthesis, increased lipid oxidation and reduced food intake [16]. Enhanced satiety may also account for the reported suppression of energy consumption but this has yet to be demonstrated.

Studies investigating the effects of HCA in humans have provided conflicting results. While some reports have shown that administration of HCA (1.2–1.5 g/day) to overweight participants did not produce any significant decrease in body weight or appetite variables [17,18], others reported that daily administration of a relatively low dose of HCA (900 mg/day) over two weeks, reduced EI and sustained satiety. It is important to note that the reduction in body weight reported in this study was only minor [19]. Preuss et al. [20] found that eight week administration of 2,800 mg/day of HCA produced a reduction of 5.4% and 5.2% in baseline body weight and BMI respectively compared to controls. HCA at those doses also reduced food intake, total cholesterol, LDL, TG and serum leptin levels, and increased HDL levels and excretion of urinary fat metabolites (a biomarker of fat oxidation). The available literature seems to support the claim that HCA may be more effective at moderating weight gain [21] than at promoting weight loss, making the compound potentially more useful for weight maintenance after an initial loss. It is important to note that some clinical studies with HCA have encountered mild adverse events such as headache, and upper respiratory tract and GI symptoms [18].

Three kinds of tea: oolong, green, and black, are widely used as traditional healthy drinks all over the world and green and oolong tea have been traditionally reported to have anti-obesity and hypolipidemic actions. Black tea also contains many active ingredients [23]; however some of these may not survive processing.

Green coffee bean extract (GCBE) (Quest Green Coffee ^®, Svetol^®) contains 10% caffeine and 27% chlorogenic acid as the principal constituents. However, the roasting process of coffee drastically reduces the level of chlorogenic acid and its related compounds [40]. The administration of instant coffee enriched with chlorogenic acid to humans induced a reduction in body fat and body mass at least in part due to a reduction in the absorption of glucose [41]. The reduction of glucose absorption would ultimately lead to an increase in the consumption of fat reserves, due to the reduced availability of glucose as an energy source [41]. Since coffee drinking and obesity appear co-existing in most developed societies the efficacy of these products in those already regularly exposed to caffeine remains to be demonstrated. However, it is important to note that a major consequence of blocking digestion of carbohydrates in the proximal gut is colonic fermentation which leads to increased microbial production of gas in the bowel; this effect can limit its use.

C. aurantium (Citrus Aurantium extract ^®, Bitter Orange extract^®) contains alkaloids such as p‑octopamine and synephrines which exert adrenergic agonist activity [42] and are present in supplements designed to aid weight loss [43]. Synephrines could potentially increase EE and decrease food intake [44]. In addition, there is some evidence that adrenergic agonists, including C. aurantium synephrines, decrease gastric motility [45].

There are a few trials that have examined the effects of C. aurantium synephrines alone, or in combination with other ingredients, on body weight and/or body composition in humans. Overall, these studies reported a loss of 2.4–3.4 kg among participants using synephrines, while placebo groups lost 0.94–2.05 kg [46]. These results point towards some beneficial effects from synephrines supplementation, however they cannot be considered conclusive at this point because they do not separate the effects of C. aurantium or synephrines from those of other ingredients, particularly ephedrine. In addition these trials were of short duration and sample sizes were frequently inadequate. Due to the above mentioned drawbacks, it would be difficult to formulate C. aurantium related public health recommendations with confidence.

Caffeine (Caffeine Pro^®) is the most widely consumed behaviourally active substance in the world [47]. Almost all caffeine consumed comes from dietary sources (beverages and food), most of it from coffee and tea [47]. The central effects of caffeine at habitually consumed doses are due to its effects on the widely distributed adenosine A1, A2A and A2B receptors [47,48].

Long-term intervention studies in humans have failed to report conclusive effects of caffeine consumption on body weight [49,50,51,52]. A possible explanation for the lack of a long-term effects could be the development of a tolerance to its effects [49]. Nevertheless, controlled experiments investigating its acute effect have found that caffeine has a small reducing effect on caloric intake [53,54,55,56]. Reintroduction of caffeine in regular coffee consumers after a period of abstinence was found to reduce the number of meals without affecting meal size, this lead to a decrease of EI [57]. Increased caffeine intake has been reported to produce slightly smaller weight gains in men and women when compared to controls [58].

Caffeine also seems to exert thermogenic and lipolytic actions [59]. However, both effects are reported to be more prominent in normal weight individuals [60,61,62]. To conclude, caffeine seems to act through central and peripheral mechanisms which would, over the long term, help with achieving weight loss. However, because of the issue of tolerance, the potential benefits of such an approach to weight control in societies of individuals already exposed to high levels of caffeine may be somewhat limited.

Nicotine is an alkaloid naturally occurring in tobacco leaves [63] and is their major addictive component. Similarly to caffeine, nicotine exerts its effect through central and metabolic actions. Among several effects, nicotine reduces appetite and alters feeding patterns typically resulting in reduced body weight [64]. Nicotine increases metabolic rate and decreasing metabolic efficiency. Smoking a single cigarette has been shown to induce a 3% rise in EE within 30 minutes [65]. In the CNS, nicotine modulates the central pathways that regulate several aspects of food intake.

In humans, numerous clinical and epidemiological studies indicate that body weight and BMI are lower in cigarette smokers than in non-smokers [66,67,68,69,70,71]. Body leanness is particularly associated with the duration, rather than the intensity of smoking [66]. In addition, smoking cessation is usually accompanied by hyperphagia and weight gain which is more prominent in women [72,73,74,75]. Nicotine administration to both smokers and non-smokers does not change hunger sensations [64]. Despite this, it decreases meal size, without substantial changes in meal number [76,77]. However, given the health and addiction issues surrounding smoking, it is unlikely that non-prescription nicotine based weight control products could enter the market without considerable demonstration of efficacy and absence of psychological side effects both during treatment and at cessation. At the moment, nicotine preparations are almost exclusively used to delay post cessation weight gain [78,79,80].

The appetite suppressant effects of chewing leaves of the khat plant (Catha edulis) have been reported for several centuries. [81,82,83]. The predominant active ingredients of C. edulis are cathinone (1-α-aminopropiophenone) and cathine (D-nor-pseudoephedrine). These compounds share similarities with amphetamine, with up to 90% being absorbed during chewing, predominantly via the oral mucosa [84]. Amphetamine-like compounds affect appetite centrally, by acting in the hypothalamus. Apart from its central effect, cathinone enhances sympathomimetic activity leading to a delay in gastric emptying [85]. In healthy volunteers, khat chewing decreased hunger and increased fullness scores, this was associated to a prolonged gastric emptying which was significant when compared to lettuce chewing [86].

H. gordonii (commercially available as pills, patches, and liquid: Hoodia pure ^® , Hoodia MAX ^® , Pure Hoodia ^® , RapidSlim SX ^®, Hooderma ^®, Hoodia-HG57 ^®), a member of the large milkweed family, is a desert-originating, succulent, slow growing plant [87]. Currently, there are more than twenty international patent applications/registrations on H. gordonii relating to the appetite suppressant, anti-diabetic activity and the treatment of gastric acid secretion [88]. The available literature offers limited reports on the biological effects of H. gordonii and its active compounds.

P57, the commercial extract of H. gordonii has been in the market for some time. It has been reported to increase ATP content in hypothalamic cells [89], which correlates with a decrease in appetite. This finding suggests that one mechanism of action of P57 is through a central mechanism; however an additional peripheral mechanism cannot be ruled out [90]. Phytopharm, who in 1997 were granted the license for the patent for the active component of the Hoodia P57 extract, have recently disclosed phase 1 studies in healthy overweight humans where significant reductions in caloric intake and body weight were achieved [91].

C. fimbriata (Slimaluma^®) is an edible succulent cactus that belongs to the family Asclepiadaceae. Its key ingredients are pregnane glycosides, flavone glycosides, megastigmane glycosides, bitter principles, saponins and various other flavonoids [92]. The appetite suppressant action of C. fimbriata could be mainly attributed to the pregnane glycosides. These compounds seem to have peripheral and central effects. In the adipose tissue, pregnane glycosides reduce lipogenesis [93,94]. In the central structures regulating appetite, pregnane glycosides and its related molecules seem to share a similar mechanism of that of H. gordonii where they act by amplifying the signalling of the energy sensing function in the hypothalamus [89,95].

In overweight humans, two months administration of C. fimbriata extracts lead to a reduction in self-reported measures of appetite, body weight and waist circumference when compared to a control group [95]. Interestingly C. fimbriata selectively reduced the intake of refined sugars, sweets, cholesterol and saturated fats, without altering fruit, vegetable or fish intake. This could provide an additional mechanism of reduction in body weight since the consumption of foods such as whole grains, fruit and vegetables has been found to be directly associated with reduction in hunger and increased satiety levels, which could lead to lowered voluntary EI [96].

C. forskohlii (ForsLean^®) is a plant rich in alkaloids that belongs to the mint family [97]. One of the main active compounds in C. forskohlii is forskolin, a diterpene that acts directly on adenylate cyclase [98]. Adenylate cyclase is an enzyme that activates cyclic adenosine monophosphate (cAMP). In turn cAMP promotes lipolysis, increases the body's basal metabolic rate, and increases utilisation of body fat [99]. Administration of C. forskohlii extract to overweight women mitigated weight gain with no significant side effects, however, weight loss was not achieved [100]. Since this preparation affected weight gain further clinical study of C. forskohlii may be worthwhile.

Although the use of cannabis (C. sativa) for medicinal and other purposes dates back at least four thousand years, understanding of the underlying pharmacology dates back only forty years. Cannabinoids are known for their rewarding effects and for their ability to stimulate increases in food intake (e.g., the marijuana 'munchies') [101]. Cannabis hyperphagia is largely attributable to Δ⁹-THC actions at brain CB1 cannabinoid receptor.

After acute and chronic administration (typically in the form of cannabis cigarettes, and less frequently oral Δ⁹-THC administration), healthy volunteers (often experienced marijuana users) increase the consumption of mainly snack food which leads to a substantial increase in caloric intake, [101,102,103,104,105,106,107]. However, it has recently been demonstrated that Δ⁹-THC can have broad, dose-related effects on appetite that are not restricted to specific flavours or food types (Townson and Kirkham, unpublished observations). Δ⁹-THC seems to predominantly enhance the hedonic value of food [108,109]. A small number of clinical trials have assessed the possible benefits of cannabinoids in the treatment of wasting and appetite loss in cancer cachexia and AIDS. Treatment with Δ⁹-THC improved appetite ratings, increased food intake, and attenuated weight loss or induced weight gain [110,111,112,113].

Sutherlandia (L. frutescens) is commonly given in the belief that this herb will treat some of the symptoms associated with HIV/AIDS, such as nausea and lack of appetite, amongst others [114]. A recent randomized, double-blind, placebo-controlled trial of Sutherlandia leaf powder in healthy adults showed that 800 mg/d during three months increased appetite ratings [115]. The constraints of the investigation related to limited sample size, precluding firm conclusions from being drawn about these preliminary data or any speculation related to mechanisms of action.