We aimed to examine the effects of different energy intakes on a range of responses that are relevant to the safety of hill walkers. In a balanced design, 16 men completed a strenuous self-paced mountainous hill walk over 21 km, under either a low-energy (1.3 MJ; 313 kcal) intake (LEI) or high-energy (12.7 MJ; 3,019 kcal) intake (HEI) condition. During the hill walk, temperatures were measured continuously, and blood samples for the analysis of metabolites and hormones were drawn before breakfast and immediately after the walk. Subjects also completed a battery of performance tests that included muscular strength, reaction times, flexibility, balance, and kinesthetic differentiation tests. During the LEI, mean blood glucose concentrations leveled off at the low-middle range of normoglycemia, whereas, on the HEI, they were significantly elevated compared with the LEI. The LEI group showed significantly slower one- and two-finger reaction time, had an impaired ability to balance, and were compromised in their ability to maintain body temperature, when compared with the HEI group. The modestly impaired performance (particularly with respect to balance) and thermoregulation during the LEI condition may increase susceptibly to both fatigue and injury during the pursuit of recreational activity outdoors.
Skipping Breakfast = Not Too Brilliant
Rampersaud's team examined the results of 47 studies on various effects of breakfast consumption among children and adolescents. Interestingly, while breakfast eaters consumed more daily calories, they were less likely to be overweight. Children who consistently ate breakfast tended to have superior nutritional profiles. This concurs with a cohesive body of data indicating that adults who eat breakfast meet their daily micronutrient needs better than habitual breakfast-skippers. Breakfast skipping also degrades mental performance in children. Overall, the evidence points to regular breakfast consumption improving cognitive function, test grades, school attendance, memory, and nutrient status. The latter effect pertains to macronutrients and essential vitamins and minerals. The impact of skipping breakfast on the intake of other functional nutrients hasn't been studied.
In a controlled intervention trial on lean subjects, Farshchi's team found that skipping breakfast decreased post-meal insulin sensitivity and increased LDL-cholesterol, despite a high (6-a-day) meal frequency. This data points to the possibility that the body is "metabolically primed" to eat a meal soon after an overnight fast.
Concurring with the above results, noted protein researcher Donald Layman asserted in a recent review that the most critical meal of the day is breakfast after an overnight fast. This is partially due to circadian protein synthesis rates being lowest at this time. He states that the anabolic impact of a meal lasts roughly 5-6 hours based on the rate of post-meal amino acid metabolism, therefore, significant dietary protein should be provided at approximately 5-hr intervals throughout the day. In the final analysis, Layman's suggestions are a safe bet without any major convenience impingements.
In three separate controlled experiments, Benton and Parker examined the effect of breakfast versus fasting on cognition. In the first study, fasted subjects took significantly more time than the fed group to complete both the spatial memory task and the word recall. In the second study measuring information processing and short-term memory decay, the fasted group lacked the improvements shown in the breakfast group. In the final trial, memory and intelligence were measured. Although breakfast didn't enhance abstract thought, it was superior to fasting for recalling a story read aloud. The researchers concluded that these trials were in agreement with a substantial body of previous research demonstrating that breakfast benefits memory.
On the observational research front, the National Weight Control Registry (NWCR) is the largest ongoing study of individuals who have successfully maintained substantial weight loss over the long term. To qualify, participants must maintain a weight loss of at least 13.6 kg (30 lb) for at least one year. According to a formal analysis led by Wyatt, 2313 subjects (78%) eat breakfast every day. Only 114 subjects (4%) reported skipping breakfast. This obviously isn’t cause-and-effect data, but it shows the crucial commonalities in the habits of dieters with long-term success. Daily breakfast is clearly one of those habits.
Fasted Exercise Training = Not Optimal
The combination of fasting and exercise training has never been a good idea from the standpoint of optimizing protein synthesis and inhibiting protein breakdown.
Recent research by Baty's team showed no exercise training performance benefit of a protein-carb solution taken pre, during, and postworkout. However, two indicators of muscle damage were elevated in the fasted training placebo group. Their myoglobin levels approached significance halfway through the exercise bout, and were significantly elevated 6 hours postexercise. Creatine kinase levels were also significantly elevated 24 hours postexercise.
Tipton's team compared the effect of an immediate PRE-excercise training dose of essential amino acids + carbohydrate with the same treatment immediately postworkout. 262% more amino acid uptake was seen in the pre-group compared to the post-group. In a subsequent study, Tipton used a similar protocol with 20g whey protein only, administered either immediately pre- or immediately postworkout. Although no significant differences in protein synthesis were seen, Tipton noted that the study was underpowered to detect differences in such a small sample size. He suggested that a protein-synthetic increase would be seen in the preworkout treatment if there were approximately double the number of subjects. Also of note is that 4 of the 8 subjects in the pre-group had greater amino acid uptake than any of the subjects in post-group. Furthermore, it’s highly likely that more protein synthesis would be seen in the pre-group if carbohydrate was taken with the protein, as was the case in Tipton’s previous study.
Bird's team saw muscle-preserving effects of an EAA+CHO solution ingested during training after a 4-hour fast [50]. The EAA+CHO treatment suppressed any cortisol increase, whereas the fasted group's cortisol levels rose 105% by the end of the training bout. 3-methylhistidine (3MH – an indicator of myofibrillar protein degredation) levels in the fasted group were elevated by 56% 2 days after the exercise bout, whereas 3MH levels the EAA+CHO group were reduced by 27%. Apparently, even a partial fast before resistance training can negatively impact muscle protein status.
