Skipping Breakfast

This is not an LC study -- indeed one could describe it as just the opposite -- but it is interesting nonetheless

Deleterious effects of omitting breakfast on insulin sensitivity and fasting lipid profiles in healthy lean women

10 healthy lean young women participated in this cross-over study (they serve as their own control and get each treatment).

Treatments:
EB = eat breakfast { cereal with low fat milk :-(  }
OB = omit breakfast  -- this group received the same meal eaten by the breakfast group later in the day.

The women selected were regular breakfast eaters prior to the study.

Essentially both groups ate ad libitum from similar foods for the remainder of the day and recorded intake.

Measurements were made of REE, TEF, EI, fasting and postprandrial insulin & glucose, and fasting lipid and uric acid levels.

Other abbreviations used:
EI = energy intake
REE = resting energy expenditure
TEF = thermal effect of food


DISCUSSION:

The aim of this study was to compare the effects of OB and EB on EI, REE, and indexes of carbohydrate and lipid metabolism and plasma uric acid concentrations. We found that, in healthy lean women, OB led to a higher plasma total and LDL-cholesterol concentrations and lower postprandial insulin sensitivity than did EB. Mean reported total EI was significantly lower during the EB period than during the OB period.  

... The mean reported EI was significantly lower in the EB period than in the OB period. This is at variance with previous studies that reported either no difference (2, 3, 9, 10) or even lower EIs (3, 10) in persons who omitted breakfast than in those who ate breakfast, despite a lower BMI in the latter group (3, 10). We did not find any differences in macronutrient composition between the EB and OB groups, which was inconsistent with the previous studies (11, 12). However, this inconsistency is likely to reflect the fact that we ensured breakfast cereal was consumed in both intervention periods; the difference was the time of its consumption. Underreporting of EIs, especially for snacks (37), might lead to errors in data interpretation and also to inconsistent results. We also had underreporting in this study, but the similar degree of underreporting between the habitual diet and the EB period, as well as the crossover design, suggests that the higher total intake in the OB period is a reliable observation even if the absolute intake is not.

... The current study did not find any difference in fasting REE and TEF between the EB and OB periods. It is suggested that, if OB has any effect on EE, a longer intervention is needed for that effect to emerge. ... Further long-term studies are required to explore the effect of breakfast consumption on EI, EE, and, finally, body weight.

...The current study reports no significant difference in fasting blood glucose and glucose profile after the test meal. These results were expected because, during short-term interventions in healthy subjects, blood glucose is likely to remain constant, and any compensation would occur via changes in insulin secretion. Furthermore, no significant differences appeared in baseline insulin concentrations or HOMA-IR values over the course of the experiment. The peak postprandial insulin response tended to be lower after the EB period than after the OB period, and the AUC of insulin profile after the test meal showed a significantly higher response after the OB period than after the EB period. Overall, we suggest that OB may reduce postprandial but not fasting insulin sensitivity in lean people. 

... Regarding the changes in plasma lipids, the present study indicates that plasma total and LDL-cholesterol concentrations increased after the OB period more than they did after the EB period. Fasting plasma HDL-cholesterol and triacylglycerol concentrations, however, showed no significant differences between the EB and OB periods. The effect of EB in reducing lipid concentration was in agreement with the findings of previous studies (11, 12, 18). However, the mechanism proposed in the previous studies, in which a lower fat intake was associated with EB, cannot explain our results, because we did not find any significant difference in total fat intake.

Insulin stimulates hydroxy methyl glutaryl-Co-A reductase, one of the rate-limiting enzymes in cholesterol synthesis. Lower total and LDL-cholesterol concentrations after the EB period might be due to a lower insulin stimulation of hydroxyl methyl glutaryl-Co-A reductase.

I've bolded selected results from the study.  I find it interesting that timing of eating seems to influence insulin sensitivity but not really sure if this has any relevance at all to low carb dietary approaches.  Jimmy Moore over at Livin La Vida Low Carb stated that there was almost unanimous opposition to intermittent fasting to treat hyperinsulinemia, and I wonder if this might be one of the reasons.

I also find interesting the energy intake -- it was significantly lower for the breakfast eaters.  As stated in the excerpt above, the researchers controlled for the cereal intake by giving the OB group the same breakfast meal later in the day.  This is actually somewhat counter to my personal experience in that on days I eat early in the day (even a good LC egg meal) I often find myself hungrier during the day.

I wonder if the results of this study do provide some rationale to eating carbs earlier in the day if you're going to eat them.  At least in this study, those eating a carby breakfast ate less overall and had better insulin sensitivity.  More importantly, there appears to be less of an insulin spike if one starts their metabolic engine earlier in the day.  Things that make you go hmmmmm...