Sugar, alcohol, caffeine & sweeteners

Ethanol yields about 7 kcal/g, sitting between carbs/protein (4) and fat (9). The body has no way to store alcohol, so the liver prioritises clearing it — oxidising ethanol to acetaldehyde and then acetate, which is burned for energy. While this is happening, the oxidation of fat (and to a degree carbs) is suppressed, so the calories you eat alongside drinks are more likely to be stored. Add that drinks are easy, liquid, non-filling calories, and that alcohol disinhibits eating, and the impact on a fat-loss effort can exceed the raw calorie count.

The old notion of a clear 'J-shaped curve' where moderate drinking protects the heart has weakened substantially as studies controlled better for confounders; current consensus leans toward 'less is better,' with no intake established as risk-free, and clear dose-dependent increases in several cancers and other harms at higher intakes. For body composition, alcohol's calories count and its metabolic priority blunts fat oxidation. None of this requires total abstinence for everyone — but it does mean alcohol is a cost to spend deliberately, not a free pass.

Caffeine blocks adenosine receptors — adenosine is the molecule that builds up through the day and makes you sleepy — so caffeine masks fatigue rather than removing the underlying need for rest. It also modestly raises adrenaline. Its half-life is roughly 5 hours but varies widely by genetics, so an afternoon coffee can still impair night-time sleep. Regular use builds tolerance to some effects (especially alertness), and abrupt cessation causes withdrawal headaches.

Caffeine is one of the best-evidenced performance aids: meta-analyses show small but consistent improvements in endurance, power, and perceived exertion, typically at ~3–6 mg/kg before exercise. Moderate habitual intake (commonly cited as up to ~400 mg/day for most adults) appears safe for the general population and is associated in cohort studies with neutral-to-favorable health outcomes. The biggest real-world downside is sleep disruption from drinking it too late — protect sleep by keeping caffeine to the morning and early afternoon.

Non-nutritive sweeteners (aspartame, sucralose, stevia, etc.) taste sweet but provide little or no calories and don't raise blood sugar meaningfully. The open questions are whether they influence appetite, sweet cravings, or the gut microbiome in ways that matter for health — biologically plausible mechanisms that have been proposed but not firmly established in humans.

Randomised trials generally show that replacing sugary drinks with non-nutritive-sweetened ones leads to lower calorie intake and modest weight loss versus keeping the sugar — a real benefit for people trying to cut added sugar. Major safety reviews have found approved sweeteners safe at typical intakes. However, some observational studies link heavy sweetener use to worse metabolic outcomes (likely confounded — people already at risk often switch to diet products), and some research raises questions about gut-microbiome effects, leaving the long-term picture genuinely unsettled. The defensible position: low-calorie sweeteners are a reasonable tool to reduce sugar, water is still the best default drink, and there's no strong evidence to fear moderate use.