Eating 700 calories a day puts you squarely in what researchers call a very low calorie diet, and people on these diets typically lose about 1.5 to 2.0 kilograms (roughly 3 to 4.5 pounds) per week. That figure comes from studies of diets in the 400-to-800-calorie range, but the actual number on your scale depends on your starting weight, body composition, how long you maintain the deficit, and how your metabolism responds. The headline rate sounds appealing, but the story behind it is more complicated than the math suggests.
What the Research Says About Short-Term Weight Loss
A review of very low calorie diets found that restricting intake to 400 to 800 calories per day increases weight loss from the 0.2 to 0.5 kilograms per week seen with traditional moderate dieting to about 1.5 to 2.0 kilograms per week.1PubMed Central. Diet and body composition. Effect of very low calorie diets and exercise At 700 calories, you’d be near the upper boundary of that range, so expecting somewhere around 1.5 kilograms a week is reasonable for the first several weeks. Over a month, that translates to roughly 5 to 7 kilograms, or about 11 to 15 pounds.
But those are averages drawn from clinical studies, and your personal results could differ substantially. A trial comparing a very low calorie diet to a moderate energy-deficit diet in obese women found the VLCD group lost about 10.9% of their body weight in eight weeks, compared to 3.9% with moderate restriction.2PubMed. The Effect of a Very-Low-Calorie Diet (VLCD) vs. a Moderate Energy Deficit Diet in Obese Women with Polycystic Ovary Syndrome (PCOS)-A Randomised Controlled Trial If you weigh 200 pounds, a 10.9% loss would be about 22 pounds in two months. If you weigh 140 pounds, it would be closer to 15. Starting weight matters enormously.
Why the First Week Feels Like a Miracle
Many people who drop to 700 calories a day report losing 5 or more pounds in the first week alone. Most of that early loss is water, not fat. When you drastically cut carbohydrates and total food volume, your body burns through its stored glycogen, and each gram of glycogen holds roughly three grams of water along with it. Your kidneys also excrete more sodium in response to lower insulin levels, pulling additional water out. The result is a dramatic drop on the scale that feels encouraging but slows considerably once those water stores are depleted.
After the first week or two, the rate of loss settles closer to the 1.5 to 2.0 kilograms per week that the research describes. Even then, the loss isn’t a smooth downward slope. Water retention can fluctuate day to day based on salt intake, stress hormones, menstrual cycle, and sleep quality, so the scale may stall or even bounce upward on any given morning even if fat loss is continuing underneath.
Not All Lost Weight Is Fat
This is the part that doesn’t get enough attention. When you eat 700 calories a day, a meaningful portion of what you lose is lean tissue, including muscle. Research on weight loss composition found that in normal-weight men who lost about 10 kilograms, roughly 40% of the total weight lost came from fat-free mass rather than fat.3PubMed Central. Weight Loss Composition is One-Fourth Fat-Free Mass: A Critical Review and Critique of This Widely Cited Rule Leaner individuals lost even more muscle proportionally: the less body fat you carry, the more your body raids lean tissue for energy.
For someone who is already fairly lean, a 700-calorie diet is particularly destructive to muscle mass. Studies of military personnel who reached very low body fat levels (around 4 to 6%) found that once they hit that floor, further weight loss came almost entirely from fat-free mass.4PubMed. Lower limit of body fat in healthy active men Your body essentially reaches a point where it won’t give up more fat and starts breaking down muscle, organ tissue, and bone instead.
If you carry a substantial amount of excess body fat, the ratio shifts in your favor. A person starting at 35% body fat will lose proportionally more fat and less muscle than someone starting at 20%. But even at higher starting weights, some lean tissue loss is inevitable on a diet this severe.
Your Metabolism Slows Down to Fight You
One of the most frustrating aspects of a 700-calorie diet is that your body doesn’t passively accept the deficit. It actively adapts to conserve energy, a process researchers call metabolic adaptation. A study measuring resting metabolic rate during calorie restriction found that adjusted metabolic rate dropped within the first three months of dieting.5PubMed. Effect of calorie restriction on resting metabolic rate and spontaneous physical activity Your body becomes more efficient at running on less fuel, which means the same 700-calorie intake produces a smaller deficit over time.
Research has quantified this adaptation at roughly 126 calories per day beyond what would be expected from the weight loss itself.6PubMed Central. The fall in leptin concentration is a major determinant of the metabolic adaptation induced by caloric restriction independently of the changes in leptin circadian rhythms In practical terms, that means your body is burning about 126 fewer calories each day than a formula would predict for someone at your new, lower weight. That gap doesn’t sound huge, but it accumulates. Over weeks and months, it significantly erodes the expected rate of loss, which is one reason why the weight loss that feels so dramatic at first eventually slows to a crawl.
The adaptation isn’t just about resting metabolism. People on severe calorie restriction unconsciously move less. They fidget less, take fewer steps, stand up less often, and generally reduce all the small daily movements that burn calories throughout the day. This non-exercise movement is a bigger contributor to total energy expenditure than most people realize, and it drops substantially when food is scarce.
Hormonal Changes That Make You Ravenous
Within just two days of severe calorie restriction, your hormonal environment shifts in ways designed to make you eat more. Research found that after two days of severe energy restriction, insulin and leptin (the hormone that signals fullness) both fell sharply, while ghrelin (the hunger hormone) and DHEA-S rose significantly.7PubMed. Appetite and endocrine regulators of energy balance after 2 days of energy restriction: insulin, leptin, ghrelin, and DHEA-S These changes happened independently of whether the participants actually felt hungrier yet, suggesting the hormonal drive to eat kicks in before your conscious experience of hunger catches up.
Leptin, in particular, plays a central role in how your body responds to a 700-calorie diet. One study found that calorie restriction dropped circulating leptin by about 44%, alongside a decrease in norepinephrine and thyroid hormone T3.6PubMed Central. The fall in leptin concentration is a major determinant of the metabolic adaptation induced by caloric restriction independently of the changes in leptin circadian rhythms Lower leptin tells your brain that energy stores are depleted. Lower T3 slows your metabolism. Lower norepinephrine reduces the “burn” side of the energy equation. Together, these create a powerful biological push toward eating more and moving less, which is part of why people on very low calorie diets often describe intense, intrusive food thoughts and difficulty concentrating on anything else.
Health Risks That Go Beyond Hunger
Severe calorie restriction carries real medical risks, and gallstones are among the most well-documented. Rapid weight loss from very low calorie diets promotes gallstone formation through two pathways: the bile becomes oversaturated with cholesterol because bile salt levels drop while cholesterol levels rise, and the gallbladder itself stops emptying properly because the low fat content of the diet doesn’t stimulate it to contract.8PubMed Central. Risk of symptomatic gallstones and cholecystectomy after a very-low-calorie diet or low-calorie diet in a commercial weight loss program: 1-year matched cohort study The faster you lose weight, the higher the risk. People who lose more than 1.5 kilograms per week, which is exactly the range a 700-calorie diet produces, are in the highest risk category for developing symptomatic gallstones.
Nutrient deficiencies are another concern. At 700 calories, it’s nearly impossible to get adequate amounts of iron, calcium, magnesium, potassium, B vitamins, and essential fatty acids from food alone. Hair loss is a common complaint among people on prolonged very low calorie diets, often showing up two to three months after the restriction begins as the body deprioritizes non-essential functions. Fatigue, dizziness, cold intolerance, constipation, and menstrual irregularities are also common.
Psychologically, the effects of severe restriction are significant. Research has linked dieting, particularly in normal-weight individuals, to low self-esteem and depressive symptoms, and severe restriction is associated with the development and maintenance of eating disorders.9Annals of Internal Medicine. Relation of dieting and voluntary weight loss to psychological functioning and binge eating The classic Minnesota Starvation Experiment, which remains a landmark reference on the effects of prolonged food deprivation, documented profound psychological changes in previously healthy young men placed on restricted diets, including obsessive food preoccupation, social withdrawal, and emotional instability.10PubMed. Physiology of weight regain: Lessons from the classic Minnesota Starvation Experiment on human body composition regulation
When Doctors Actually Prescribe These Diets
Very low calorie diets aren’t something researchers invented to torture volunteers. They have legitimate clinical applications, typically for people with obesity-related conditions where rapid weight loss offers clear medical benefits that outweigh the risks. The most promising recent application has been in type 2 diabetes remission. Evidence from comprehensive randomized controlled trials found that a very low calorie diet intervention led to diabetes remission in 45 to 60% of subjects after 12 months, with about 35% maintaining remission at 24 months.11PubMed Central. Remission of Type 2 Diabetes with Very Low-Calorie Diets—A Narrative Review
In these clinical settings, the diet is medically supervised, usually relies on specially formulated meal replacements to ensure adequate protein and micronutrient intake, and is time-limited (often 8 to 12 weeks) before transitioning to a more moderate eating plan. The supervision matters: regular blood work monitors electrolytes, liver function, and cardiac health. This is fundamentally different from someone deciding on their own to eat 700 calories a day using whatever food they happen to have.
Protecting Muscle During Severe Restriction
If you’re going to eat 700 calories a day despite the risks, two strategies can reduce the proportion of muscle you lose. The most effective is resistance training. A review of the evidence concluded that resistance exercise is effective at slowing or even preventing the loss of muscle mass during weight loss, while the effects of endurance exercise (like running or cycling) on preserving muscle are unclear.12Advances in Nutrition. Preserving Healthy Muscle during Weight Loss Lifting weights sends a signal to your body that the muscle is being used and shouldn’t be broken down for fuel.
The second strategy is protein intake. A review of very low calorie diets emphasized that priority should be given to resistance exercise training, with adequate protein intake as a secondary but important factor for mitigating muscle loss.13PubMed Central. The impact and utility of very low-calorie diets: the role of exercise and protein in preserving skeletal muscle mass In practice, on a 700-calorie diet, this means devoting a large proportion of those calories to protein, ideally spreading it across multiple meals. The challenge is obvious: when total calories are this low, allocating enough to protein leaves very little room for fats and carbohydrates, which makes the diet even more restrictive and harder to sustain.
Even with both strategies in place, some muscle loss is virtually guaranteed at this level of restriction. You’re mitigating the damage, not eliminating it.
Why Most People Regain the Weight
The long-term track record of very low calorie diets is poor. A comprehensive review of the biology of weight regain concluded that most obese individuals eventually regain the weight they lost, and that the biological response to weight loss involves persistent and redundant adaptations in energy balance that drive the high rate of recidivism.14PubMed Central. Biology’s response to dieting: the impetus for weight regain The word “redundant” is key: your body doesn’t rely on just one mechanism to push you back toward your previous weight. It uses the metabolic slowdown, the hormonal shifts, the increased hunger drive, the reduced spontaneous movement, and the muscle loss (which further lowers your calorie needs) all at once.
The hormonal changes described earlier don’t fully reverse when you return to normal eating. Leptin can remain suppressed for months, and the metabolic adaptation persists well beyond the period of active dieting. This means that when you go back to eating 1,800 or 2,000 calories, your body is burning fewer calories than it was before the diet and simultaneously driving you to eat more than you normally would. The combination creates conditions that strongly favor regain.
This doesn’t mean weight loss is impossible to maintain, but it does mean that losing 20 pounds on a 700-calorie diet and then returning to your old eating habits is almost guaranteed to result in regaining most or all of that weight within a year or two.
What Happens Inside Your Gut
An emerging area of research involves how severe calorie restriction affects the gut microbiome. A study tracking the fecal metabolome of overweight subjects during a six-week very low calorie diet found decreased levels of short-chain fatty acids after weight loss.15European Food Research and Technology. Impact of a 6-week very low-calorie diet and weight reduction on the serum and fecal metabolome of overweight subjects Short-chain fatty acids are produced by gut bacteria when they ferment dietary fiber, and they play roles in gut barrier integrity, immune regulation, and even appetite signaling. When you eat very little food, and particularly very little fiber, the microbial community that produces these compounds gets less fuel to work with.
The long-term implications of these gut changes are still being studied, and researchers found significant individual variation in how the metabolome responded to weight loss. Some people’s gut chemistry shifted more dramatically than others, suggesting that the microbiome may be one of the factors that explains why two people on identical diets can have very different outcomes. The science here is young, but it adds another layer to the picture of what severe restriction does to your body beyond what the bathroom scale reflects.
How Your Starting Body Composition Changes the Math
Two people eating the same 700 calories a day can have vastly different experiences depending on how much body fat they carry at the start. Someone beginning at 40% body fat has extensive energy reserves their body can draw from, which means a higher proportion of the weight lost will be actual fat and the hormonal distress signals will be somewhat less intense. Someone starting at 18% body fat is already relatively lean, and their body will defend its remaining fat stores far more aggressively.
Research on this relationship found a strong positive correlation between starting body fat percentage and the proportion of weight lost as fat-free mass. Men who began with lower body fat lost a larger share of their weight from lean tissue.3PubMed Central. Weight Loss Composition is One-Fourth Fat-Free Mass: A Critical Review and Critique of This Widely Cited Rule The practical takeaway: if you’re already at a healthy weight and considering 700 calories a day to get leaner, a disproportionate amount of what you lose will be muscle. The people who can tolerate very low calorie diets with the least collateral damage are those who have the most excess fat to lose, and even for them, medical supervision and a clear time limit make the approach substantially safer than going it alone.