Table 2 Diet categories

Low-energy diets (LED)

LED: 800–1200 kcal/day

VLED: 400–800 kcal/day

Rapid weight loss (1.0–2.5 kg/week, diets involve premade products that eliminate or minimize the need for cooking and planning.

VLED have a higher risk for more severe side-effects, but do not necessary outperform LED in the long-term

Low-fat diets (LFD)

LFD: 25–30% fat

VLFD: 10–20% fat

LFD have the support of the major health organizations due to their large evidence basis in the literature on health effects. Flexible macronutrient range. Does not indiscriminately vilify foods based on CHO content.

Upper limits of fat allowance may falsely convey the message that dietary fat is inherently antagonistic to body fat reduction. VLFD have a scarce evidence basis in terms of comparative effects on body composition, and extremes can challenge adherence.

Low-carbohydrate diets (LCD)

50–150 g CHO, or up to 40% of kcals from CHO

Defaults to higher protein intake. Large amount of flexibility in macronutrient proportion, and by extension, flexibility in food choices. Does not indiscriminately prohibit foods based on fat content.

Upper limits of CHO allowance may falsely convey the message that CHO is inherently antagonistic to body fat reduction.

Ketogenic diets (KD)

Maximum of ~50 g CHO

Maximum of ~10% CHO

Defaults to higher protein intake. Suppresses appetite/controls hunger, causes spontaneous reductions in kcal intake under non-calorically restricted conditions. Simplifies the diet planning and decision-making process.

Excludes/minimizes high-CHO foods which can be nutrient dense and disease-preventive. Can compromise high-intensity training output. Has not shown superior effects on body composition compared to non-KD when protein and kcals are matched. Dietary extremes can challenge long-term adherence.

High-protein diets (HPD)

HPD: ≥ 25% of total kcals, or 1.2–1.6 g/kg (or more)

Super HPD: > 3 g/kg

HPD have a substantial evidence basis for improving body composition compared to RDA levels (0.8 g/kg), especially when combined with training. Super-HPD have an emerging evidence basis for use in trained subjects seeking to maximize intake with minimal-to-positive impacts on body composition.

May cause spontaneous reductions in total energy intake that can antagonize the goal of weight gain. Potentially an economical challenge, depending on the sources. High protein intakes could potentially displace intake of other macronutrients, leading to sub-optimal intakes (especially CHO) for athletic performance goals.

Intermittent fasting (IF)

Alternate-day fasting (ADF): alternating 24-h fast, 24-h feed.

Whole-day fasting (WDF): 1–2 complete days of fasting per week.

Time-restricted feeding (TRF): 16–20-h fast, 4–8-h feed, daily.

ADF, WDF, and TRF have a relatively strong evidence basis for performing equally and sometimes outperforming daily caloric restriction for improving body composition. ADF and WDF have ad libitum feeding cycles and thus do not involve precise tracking of intake. TRF combined with training has an emerging evidence basis for the fat loss while maintaining strength.

Questions remain about whether IF could outperform daily linear or evenly distributed intakes for the goal of maximizing muscle strength and hypertrophy. IF warrants caution and careful planning in programs that require optimal athletic performance.