"People who use the artificial sweetener aspartame are better off consuming sugar, since aspartame can actually contribute to weight gain rather than weight loss. For example, high levels of aspartame have been shown to trigger a craving for food by depleting the brain of a chemical that registers satiety, or the sense of being full. Furthermore, studies suggest that sugars, if consumed after at least 45 minutes of continuous exercise, actually enhance the body's ability to burn fat. Consequently, those who drink aspartame-sweetened juices after exercise will also lose this calorie-burning benefit. Thus it appears that people consuming aspartame rather than sugar are unlikely to achieve their dietary goals."

The author argues that the people who consume aspartame are better off consuming sugar as it contributes to weight gain. This claim has unwarranted assumptions that aspartame will have the stated benefit. He further states that sugar, in contrast, has the ability to burn fat and that people who consume aspartame after exercise are unlikely to achieve their dietary goal. This conclusion is weak as the author assumes that aspartame has no benefits other than fat gain.
Firstly, the author's cites an example where he talks about how aspartame works. He fails to talk about the side effects of consuming aspartame, which could be fatal. In such a case, intake of aspartame could be harmful, rather than being beneficial. Furthermore, the author mentions high level of aspartame intake, but gives no information about the quantity permissible to have benefial effect. Additionally, how much weight can be gained by consuming aspartame. The claim made by the author here, lacks substantial evidence.
Secondly, the author ignores the possibility that aspartame could have other benefits, such as those of sugar, to enhance body's ability to burn fat, if consumed differently or in different quantity. The authors claim that sugar if consumed after at least 45minutes of exercise would help in burning calorie is weak , since it does not mention the quantity if sugar permissible to have benefits rather than increase the risk of diabetes. Moreover, he states that those who drink aspartame-sweetened juices, will not have the effect of calorie burning. He fails to justify the effect aspartame would have if it is consumed in other forms such as tablets, food, or other beverages.
As it stands, the argument is flawed for the reasons indicated. The argument could have been strengthened, had the author provided more information about the levels of aspartame to consume, and its further benefits and risks. It could have also been strengthened, had the author provided substantial evidence to claim that if a person consumes aspartame instead of sugar, he is unlikely to achieve his dietary goal.