Not eating enough calories?

SerenityPhoenix

I'm supposed to eat about 2000(1200 normally) calories a day according to MFP when I work out. According to my BMR I'm suppose to eat 1819 and my TDEE is 3138. Yesterday, I barely got over 1200 calories and I did work out. What will happen if I don't eat enough calories? Can someone explain this to me?

jaz050465

There are loads of posts on this. Do a search for eating exercise calories. Opinion is split!!!

AntWrig

I'm supposed to eat about 2000(1200 normally) calories a day according to MFP when I work out. According to my BMR I'm suppose to eat 1819 and my TDEE is 3138. Yesterday, I barely got over 1200 calories and I did work out. What will happen if I don't eat enough calories? Can someone explain this to me?

Prolonged low calorie dieting and excessive amounts of cardio leads to metabolic damage. Regarding the comment about "opinions being split". You have people accepting facts and you have others in denial.

Justkritter

I'm supposed to eat about 2000(1200 normally) calories a day according to MFP when I work out. According to my BMR I'm suppose to eat 1819 and my TDEE is 3138. Yesterday, I barely got over 1200 calories and I did work out. What will happen if I don't eat enough calories? Can someone explain this to me?

If you work out and you don't eat enough calories this can lead your body to reduce its metabolism and maybe even lose your muscle mass since it will resort to it to get the needed energy. Been there done that. If you can't really reach 2000 then maybe at least go past 1500 if you do workout like 3-5 times a week just to keep your energy up and to provide your body with enough nourishment to repair and grow your muscles. Sometimes eating a lot more can also lead to weight loss with proper workout.

LIttleCamel

I used to struggle to eat 1200 calories, try adding calorie dense food into your diet (avocado, olive oil, nuts, etc).

It's important that you eat enough food. Whilst I lost about 15kg by barely eating 1200 calories a day, a lot of it was lean muscle. I regret that and am now trying to rectify it!

geekyjock76

Setting the appropriate deficit for the individual based on their fat mass and activity level is important. The amount of fat mass a person has dictates how much total fat mass that can be oxidized to meet energy needs in a 24-hour period. There was a study done and the basic formula is: 31 cal x lbs of total fat mass. That will give you the theoretical maximum deficit in which fat stores will be used - anything greater, and your body will no longer burn additional fat in the same day. Thus, the smaller the deficit, the less lean body mass will be used as fuel, regardless of degree of fat mass; in contrast, the larger the deficit building up to that limit on fat oxidation will incur a greater ratio of lean body mass loss.

With the above in consideration, it goes without saying the more fat mass a person has, the larger the deficit he/she can safely assume and maintain with relative preservation of lean body mass with moderate decline in Resting Metabolic Rate. In addition, impairment in hunger signalling due to a dramatic decrease in leptin is also present in VLCDs.

Here is a study you may find interesting:

Metabolic Slowing with Massive Weight Loss despite Preservation of Fat-Free Mass

Abstract

Context: An important goal during weight loss is to maximize fat loss while preserving metabolically active fat-free mass (FFM). Massive weight loss typically results in substantial loss of FFM potentially slowing metabolic rate.

Objective: Our objective was to determine whether a weight loss program consisting of diet restriction and vigorous exercise helped to preserve FFM and maintain resting metabolic rate (RMR).

Participants and Intervention: We measured body composition by dual-energy x-ray absorptiometry, RMR by indirect calorimetry, and total energy expenditure by doubly labeled water at baseline (n = 16), wk 6 (n = 11), and wk 30 (n = 16).

Results: At baseline, participants were severely obese (×± sd; body mass index 49.4 ± 9.4 kg/m2) with 49 ± 5% body fat. At wk 30, more than one third of initial body weight was lost (−38 ± 9%) and consisted of 17 ± 8% from FFM and 83 ± 8% from fat. RMR declined out of proportion to the decrease in body mass, demonstrating a substantial metabolic adaptation (−244 ± 231 and −504 ± 171 kcal/d at wk 6 and 30, respectively, P < 0.01). Energy expenditure attributed to physical activity increased by 10.2 ± 5.1 kcal/kg·d at wk 6 and 6.0 ± 4.1 kcal/kg·d at wk 30 (P < 0.001 vs. zero).

Conclusions: Despite relative preservation of FFM, exercise did not prevent dramatic slowing of resting metabolism out of proportion to weight loss. This metabolic adaptation may persist during weight maintenance and predispose to weight regain unless high levels of physical activity or caloric restriction are maintained.

http://jcem.endojournals.org/content/early/2012/04/24/jc.2012-1444.abstract?rss=1

Now, the reason why VLCDs result in people regaining the weight back with even higher fat mass:

Autoregulation of body composition during weight recovery in human: the Minnesota Experiment revisited.

Abstract
OBJECTIVES:
To gain insights into the control systems underlying human variability in the regulation of body composition during weight recovery, as well as the disproportionate recovery of fat relative to lean tissue, the classical Minnesota Experiment conducted on 32 men subjected to long-term semi-starvation and refeeding was revisited with the following objectives: (1) to determine whether the control of energy-partitioning between lean and fat tissues during weight loss and weight recovery is an individual characteristic, and if a predictor can be statistically identified, (2) to determine whether the reduction in thermogenesis during weight loss persists during weight recovery, and underlies the disproportionate recovery of fat tissue and (3) to integrate the control of energy-partitioning and that of thermogenesis in order to explain the pattern of lean and fat tissue mobilisation and deposition during weight loss and weight recovery.
METHODS:
Individual data on body weight, body fat, fat-free-mass (FFM), and basal metabolic rate (BMR), assessed during the control baseline period (i.e. prior to weight loss), at the end of 24 weeks of semi-starvation, and at the end of a 12 week period of restricted refeeding, were used to calculate the following parameters: (i) a quantitative index of energy-partitioning, the P-ratio, defined as the proportion of body energy mobilised as protein during weight loss, or as the proportion of body energy deposited as protein during weight recovery, (ii) a quantitative index of changes in thermogenesis, defined as the change in BMR adjusted for FFM (or for both FFM and fat mass) and (iii) the degree of replenishment of fat and FFM compartments, defined as the recovery of body fat and FFM (during refeeding) as a percentage of that lost during semi-starvation.
RESULTS:
This re-analysis indicates the following: (i) a large inter-individual variability in P-ratio during both weight loss and weight recovery, but for a given individual, the P-ratio during refeeding is strongly correlated with the P-ratio during semi-starvation, (ii) body composition during the control period is the most important predictor of variability in P-ratio, such that the higher the initial % body fat, the lower the proportion of energy mobilised as protein, and hence the greater the propensity to mobilise fat during semi-starvation and to subsequently deposit fat during refeeding and (iii) at week 12 of refeeding, the change in adjusted BMR is found to be reduced by a magnitude which is inversely proportional to the degree of fat recovery, but is unrelated to the degree of FFM recovery. A quantitative relationship is derived between the P-ratio during refeeding, the % fat recovery, and the P-ratio during semi-starvation.
CONCLUSIONS:
Evidence is presented here suggesting that (i) human variability in the pattern of lean and fat tissue deposition during weight recovery is to a large extent determined by individual variations in the control of energy-partitioning, for which the initial % body fat is the most important predictor and (ii) the disproportionate gain in fat relative to lean tissue during weight recovery is contributed by a reduction in thermogenesis (i.e. increased efficiency of food utilization) for accelerating specifically the replenishment of the fat stores. These control systems, operating via energy-partitioning and thermogenesis, have been integrated into a compartmental model for the regulation of body composition during underfeeding/refeeding, and can be used to explain the individual pattern of lean and fat tissue deposition during weight recovery in situations ranging from the rehabilitation after malnutrition to the relapse of obesity.

http://www.ncbi.nlm.nih.gov/pubmed/8696417